Now then, I'll go into more detail in your individual points in a second post but due to the length I'll dedicate this first one to this attempt at making the game work with your style.
So, Babylon, Huge Earth, Emperor, 24 City states and 11 Civs, Abundant resources with infoaddict and a mod that disables the maps from ancient ruins.
I'll show the early lay of the land, this map was taken from a screenshot at turn 142 but just showing a few borders won't give much of an idea what we're dealing with.
B is Babylon
A is Akkad, the second city
D is Dur Kurigalzu, the third
CS and CS2 are Helsinki and Bucharest
Blue M is Mongolia
Yellow R is Siam
Green H is the Iroquois
Blue W is China
Pink smiley face is Monty
I founded Babylon next to a river and on some sugar with 2 more next to it and a gold mine 2 tiles away, as always I start off with 2 scouts, one of which promoted via ruin to a Babylonian Bowmen, I figured I should get some culture rolling so I made a monument and opened Tradition, first rushed to Great Library as I find it's hard to get if not made emediate priority, I wanted to get a worker from a CS but appearantly they had other priorities as well.
So after a bit of scouting I find 3 patches of Dye, with 3 more that could be annexed via culture bombing CS's, hardbuild a settler and found Akkad.
The beginning was fairly uneventful, I stole a worker from Helsinki, shown as CS on the map which Lizzy told me off for but she didn't even bother with a denouncement, Napoleon did some fighting with Lizzy and Darius with Siam but nothing much happened as they where all too weak to actually take any cities.
And then I find Monty with a big trollface, the city shown belonging to him on the map was founded later then Akkad, but ofcourse gave him more then enough reason to make me his first priority.
Montezuma was friendly so I figured he was gonna backstab me any moment, so I prioritized iron working and getting the free Liberty settler to pop just after I knew where the closest iron was, which in this case was in a desert, not the best position but you have to make due when Monty is your neighbour, Dur Kurigulza was founded.
Monty Declares, not to my surprise, I didn't even mind, blaming Monty for DoW'ing you is like blaming a dog for licking his balls, and you know he'll never take your cities as he just brings jaguars and the occasional archer, none of which actually managed to get a single hit in on my 2 archers or Akkad itself, that I had conveniently placed behind a river from his perspective ofcourse helped but generally he actually manages to at least get a few hits in on the city.
They just waited, trying to circle around to 2 tiles away from the city, waiting for the rest to come join them while I picked them all off, I started to fear they might have tried to fix the AI but only managed to destroy it but Monty is always a special case so I went on, fighting off his jaguar hordes and levelling up some archers while I connected the iron from Dur.
Just some quick backgrounds on the nations, Lizzy was being a warmonger, deprived of any real coasts, spawning aproximate Moscow, mostly made army and was warmongering it up with a lot of archers and the occasional pikeman, she'd been in a couple of wars with Napoleon but diplomatically, according to infoaddict at least, noone minded.
Genghis was attempting to murder city states and building wonders, I hadn't seen much of him, his city closest to mine was founded a lot later then Dur, but he still told me how I broke my promise not to settle close to him. I vaguely remember him warring with Siam as well, but nothing much came of it, like most of the AI's endeavours.
Siam was going heavy culture and allied most of the city states I managed to find, he was warring with Persia, his western neighbour and had insane amounts of money, making him a good trading partner, he was always ahead in policies but had almost no culture boosting buildings and not a single wonder, all of it came from his CS and policies.
Hiawata seemed to be the isolated Civ, he spawned in south Africa so he did have borders with Siam but they never declared war (or friendship), I guess the AI does'nt mind if it's one of themselves, he was heavily tech focussed and even when I started to rise above the AI's cheating and overtaking them in tech he stayed ahead of me for a while.
Wu was going wonder focussed, taking the Hanging Gardens and one of the DLC wonders before I could get them, she only had 3 cities though.
France and Persia never got off the ground, I would occasionally trade with them but that's about all of it.
And ofcourse Monty was being Monty, DoW and denouncement galore, knowing him his cities are pretty useless though so I figured it's better to let him do his thing and hope he gets tired of me eventually, taking or razing his cities would probably just make me into the warmonger (mind you, noone disliked Monty, havn't seen a single denouncement until he started attacking city states and Siam).
When I looked at their relations with me, most of them coveted my lands, even England and Siam who where miles away, perhaps this was an unlucky AI roll?
I'll try to summarize the first part of my diplomacy in this game, trade stuff, Monty becomes friendly, Monty backstabs, Monty makes peace, Monty Denounces, cascade of denouncements, cascade of DoW's, the biggest problem here was Siam, 2 of the city states next to me where peace blocked because they where allied with him, Helsinki to the East and Bucharest to the north, being annoyed by the city states because they where choking off the ol' 'lebensraum' and not wanting to deal with another opponent hitting Akkad I quickly took out Helsinki with some bow and swordsmen and after fighting back Wu's archers from north I took out Bucharest and after that Shanghai.
This is about when the combined Mongolian-British forces hit on Dur, my iron city, this screenshot should give a fairly good idea of the mental state I was in at this point.
At this point I've killed of a few pikemen and archers that they have been sending my way haphazardly, again, with the archers not doing a single attack, only the occasional pikeman would suicide himself against the walls, just waiting for the rest of the immense army, that is too big to get a proper concave for the entirety anyway, to reach them to commence attacking (or at least that's what I assume).
They did manage to kill an archer that was standing on that hill with the half constructed fort, but thats all the damage they did. Ofcourse the citadel helped a lot but most of them where not even in it's range.
3 turns later, it looked like this:
The stragglers where dispersed and dealt with swiftly.
Seeing their armies dwindle, England and Mongolia made peace for peace, the Aztecs had been crushed a while ago and we had since been at peace, while Siam and Hiawata wanted everything I had for peace, for Hiawata this was not a problem as he was too isolated to be a threat anytime soon, despite his strong tech, but Siam still had control over most of the city states, making it impossible for me to even try to engage in diplomacy via them.
Figuring the warring would take a while I should at least take down some of the attacking potential of the enemy, so I took Beijing, a very strong city in the north with 2 wonders and good infrastructure and started marching on Genghis, who was just now getting himself Keshiks, making him somewhat of a priority, I burned his closest 2 cities in the desert and made a single one that could annex 4 silver 3 insence and a gold, I then took another 2 big cities and he offered all his cities for peace, I burned all the useless stuff, setting me back to -60 happiness initially, and while I was consolidating and trying to get the Forbidden Palace to fix my happiness problems that bastard built it.
During this time Hiawata became active, I'd wondered when his death army would come rolling down, appearantly he wanted to do an amphibious invasion, this ofcourse was swiftly dealt with by some caravels purely for this purpose.
I should note here that Karakorum was as well defended as you can get get, apart from the Forbidden palace he also made the Kremlin and Himeji Castle, getting an insane 55 or so defence while all the other capitols where still around 30, and the place was surrounded by forests.
I lost about 4 or 5 units taking it but when it was done the Forbidden Palace fixed my entire happiness problem like I'd hoped.
Ofcourse while I was taking care of the mongols the chinese saw the opportunity and tried to take back their lost land, when I saw their force I was pretty certain I would lose it:
But again, they just stood there, NOT FIRING! This is ridiculous, from what I recall the AI would at least fire at a city when it had the opportunity, not fortify and wait while being in range of bow or cannonfire, despite their pikeman being on their way I guess they where waiting for it to arrive before attacking.
The Chinese uprising was slaughtered and she left me alone for the rest of the game, especially since my universities where getting finished and giving me massive tech boosts.
After murdering Genghis's cities I went onwards to Siam, after murdering the Mongols everyone but Hiawata, I'm guessing because he was only marginally behind in tech and had a huge spam army, mostly cannons, longswords and knights at that point, all of which while still keeping a very strong tech and culture rating and having a couple of CS buddies.
I'd also found the rest of the Civ's, I've often had situations where the dominant American Civ will pose a real threat, but in this case they where just messing around, Japan, the Inca and Arabia where always behind in practically everything and apart from some trading and the occasional denouncement they where of no value and will not be referred to anymore.
At this point I had to choose how to deal with Hiawata, either go for an overseas invasion, with all the risks and hassle that that entails or plow my way through the relatively soft target Rammy.
Before I even got to him, having to take out the 2 city states blocking the arabian peninsula, Hiawata figured out he'd lose less of his forces trying to take me out by simply travelling through Rammy's territory so I had to fight off waves like this about 10 times while slowly advancing and taking the Thai cities to get to my intended target.
Again, there is no semblance of composition, he did not get in a single hit before I was halfway through Africa, had just taken a city state that he reconquered the turn after, that I then conquered again and he was able to take again until I eventually managed to take it for good, leaving Dublin with 1 pop.
2 of the 3 unit's I lost in the entire war, killing hordes of Hiawata.
Eventually I got to his actual homeland, due to rather convenient placement I could emediatly go for his capitol, yet he still refused any kind of peace treaty that was not in his favor.
Eventually I took all of his remaining cities out of spite, I'd spent too much time to not see him grovelling about how much of a failure he was, in the couple of remaining turns I had I murdered off Siams new capitol as the bastard built the Eifel tower, which I'd hoped would get me out of the unhappiness all those new cities caused.
Because I plowed through Siams land rather quickly, not bothering with any city that was not needed on my way to the real target he had a couple of cities on the east coast of arabia that he had no more access to, suddenly Monty declared war on him and completely murdered the places with hordes of riflemen.
This is the only conquering I've seen the AI do in the entire game, apart from Pacahuti, who I believe managed to conquer a rather small Arab city at a certain point all AI conquest heavily failed, and only because he was not using any ranged units that would just have stood there picking its nose.
I find it fitting that Monty, the first guy to DoW me would eventually become my only friend, at least when he was done warring for a bit he would be friendly or at least allow better trade prices then the other Civ's, hating me for 4/5th of the time is still better then the constant hate I got from the other ones.
Admittedly friend might be a big term but I've always enjoyed Monty, sentimentalism combined with the only Civ to have a opportunistic tendency that is not purely aimed at me is very refreshing.
Eventually I ended the game 10 or so turns after wiping out Hiawata via spaceship victory, which I probably could have delayed for a pretty long time as noone was getting even close to a victory (Hiawata was the only one who was even close to being able to building the UN apart from me, and with Siam being a CSmonger I was not very inclined to build the UN for him).
A game where I intended to get myself to engage in diplomacy eventually ended with me owning half of Asia and most of Africa and having taken 4 capitols and 4 city states.
If I'm to reflect on what went wrong, I'd say that purely being in a war with Monty might have given them several length of war modifiers and refusing his peace treaties that asked for everything I had probably added another, then perhaps his denouncement and me stealing a worker from a CS might have given another that might have triggered the cascade, possibly fueled by me having a relatively small army (altough you can't get a big army compared to the AI on emperor without sacking everything else, they produce absurd amounts of military).
Trying for diplomacy feels like walking a tightrope because the AI get's ticked off by too many things, most of which are out of your control, if you'd provide some insight into how you would have made this work that would be great, as the only thing I can think of is staying on a single city and not spawning next to Monty.