@MarkM
I'm not sure how helpful this will be. I didn't have that option set. (I'm going to set it now. Could be useful in the future.)
All I have is the 4000BC autosave of the last attempt I made - which was (almost laughably) not so close to the real start.
I've attached a screenshot - after the scout moves to show some resources that convinced me to try the game - and the start save.
As you can see, there are some vital differences. Plains instead of grass. Coastal start instead of 'perhaps coastal'.
Thank you very so much AgedOne! Sorry my gratitude is belated but I wasn't able to get to play it until last night, didn't have much time to play last 10 days and the time I had I spent finishing GOTM16. Also thanks to RobertTheBruce, though I haven't yet looked at yours I will. It sounds "intriguing" based upon others' comments!
I've never gone beyond Monarch (well maybe emperor once a long time ago in vanilla, and I didn't fare well) & usually a builder -- I'm just starting to try to consciously move away from that tendency in last couple GOTMs. So this is going to be a stretch for me. I figured my actual game would be brief

so might as well put some extra time in on the front end to get more out of dissecting my defeat

When I played your map though I was surprised to find I wasn't immediately wiped out. While I definitely wasn't doing WELL (was in 2nd to last at ~500BC, with half the score of the leader), I had successfully attacked Mansa Musa & razed 3 of his cities + captured a 4th, leaving him with one. Given that my scout had encountered him a turn ~12 & he already had a skirmisher I was pleased I could even overcome the big early lead he had.
However I'm still on the road to nowhere in this game. At 500 BC I have a respectable army in quantity, but it soon will be lagging in quality, it's pretty much immortals, swordsmen, and a couple archers and axemen. My problem is that my maintenance is killing me, even at 0% tech research I still only generate a surplus of 1 gp per turn!

I have 4 cities, capital + 3 others 5-8 squares away.. I don't see it as a mistake to have any individual one of these cities -- #2 and #3 were need to hook up critical warmaking resources of horses and iron respectively (I started the war with just immortals, but quickly found I lost at least one for each skirmisher defender, to soften it up, so I think the swordsmen I got from hooking up the iron really improved my military position, especially when given mansa started building spearmen just after that; his remaining city is built right on top of an iron deposit). I thought I was very selective in keeping captured cities -- as I mentioned I razed 3, and the last one is not only close to the capital & on the nicest site of all my cities (it will produce lots of commerce if i can ever get it going), but it is also the jewish holy city & my only city with religion currently. But yet I'm basically mired down -- can't build much else but early military units because of lagging tech, can't do more research because of maintenance, can't boost commerce much because I pursued military techs & haven't got pottery or writing yet, and finally can't get techs out of mansa in a peace deal (he clearly has them, he has built cottages & has ships sailing around i can't build, and since I have him down to 1 city & a healthy lead in score on him still, I think he'd buy me off with them) because I don't have alphabet yet.
Anyway, what am I asking? I think it comes down to this: is it possible to go TOO much a warmonger at Immortal level, is that my problem? Did I need to obtain research infrastructure advances (pottery, writing) earlier, work commerce squares earlier to accelerate getting those techs, and focus less on working production tiles? That's something I think I have been able to overcome in my warmongering attempts on lower difficulties (= lower maintenance), but has trapped me here. In particular having alpha not much beyond the start of your first major war seems like a good idea to get the most out of wars (getting good peace terms). I think I still need to find a balance here... I'm gonna try one of RobertTheBruce games next, maybe Thursday night, and I think I'll try to do those things, modified by whatever advice I might get here. Looking at the starting position for the WOTM in particular, it makes me think moving to the coast might be advisable not only for reasons discussed here but to boost early commerce/tech research, as well as the other advantages talked about already here. The starting position looks pretty light on early research possibilities, except for the lake. Maybe horses & iron will turn up in starting radius so I won't have to build those early extra cities though ...
I realize most readers are probably playing WOTM7 already, but any general advice is appreciated.