Gonna dig into the save and make a fairly lengthy set of comments; sorry if this ends up a little disorganized.
Industrious Forges when you have gold and gems are a good building, but right as you start a war is not the time to begin them. For that matter, you're not that crunched for happiness. About to get Ivory in Huamanga, that's +1 happiness to all cities. Calendar will get you silk and Incense when Machu Picchu's borders expand in 13 turns. Ethiopia has Monarchy; with any luck you can extort it out of them in a peace deal and start getting wine for another +1 happiness. The silver and fur to the northeast is still unclaimed for whenever you get around to it; dropping a couple cities up there will cost less than building 5 forges, which you're doing right now. Right now you need more military units, and if you're happy with how many military units you have I'd prioritize settling the northeast (silver/corn, crab/deer/furs) and getting more workers out (you have multiple cities working unimproved tiles, which should always be a red flag to either whip more population away or build more workers).
That army is a bit dicey. You're looking at 4 turns moving your army to the capital, 2 turns bombarding city defense away, and 1 more turn actually assaulting the city (start by sending in a couple catapults to soften the stack up). 4 catapults, 3 axes, and 4 chariots isn't exactly overwhelming force, especially when Ethiopia can research Feudalism (you can check that in the f4 foreign advisor screen) so those archers might get a surprise upgrade to longbows. It'll probably work here, but... it's not even half the size you'd really prefer.
Speaking of hitting earlier. When you are planning to attack someone, commit to the prep. No half-measures; if you're going to war, go all in. It's okay to stack 2 or 3 whip unhappiness at a single city. You don't want to whip with zero hammers invested (there's a penalty for that), but it may be okay to whip every second turn for a bit when putting together an army. And if ever there's a time to chop your forests, that's it. If you do 2 2-pop whips each in Ollantaytambo, Machu Picchu, Corihuayrachina, 3 in Cuzco, 3 in Tiwanaku, had your 9 workers chop a forest each, used 160 gold to upgrade a pair of Quechua to axes, and pulled in your chariots, in less than 10 turns you could have pulled together something like 10 catapults, 12 axes, and a half-dozen chariots. Yes, that would have temporarily slowed your economy, but you'd have an army that would crush Ethiopia and with modest reinforcements might well be able to carry on to take out Genghis Khan and Justinian as well.
The Quechua on Ethiopia's iron does nothing. Move him to somewhere like the forest 1E of the corn and he actually blocks out a decent region where barbarians can no longer spawn, or upgrade him to an axe and have him join your army. I'd also upgrade the other Quechua up there to an axe so he's a more reliable barbarian defense. Right now if a random barb warrior shows up and kills him, that's a big loss - you might outright lose Corihuayrachina.
Corihuayrachina is growing past its improvements. Be better to either get a worker or whip the pop towards something useful instead of growing in size that fast. The farm should be 1E of the lake, not 1W; that way it spreads irrigation to the east, where you can eventually use it to irrigate that corn. That barb city northwest of it is inconvenient; ideally you'd have wanted to put a city 1NE of that spot where it gets crab, deer, and fur (chop + whip a library, whip a work boat, work deer + crab + 2 scientists and forget about the city). Since you've got some empty land with good resources to the northeast, maybe build axemen (to fill out the area preventing barb spawns) and/or settlers there. It's a bit late in the game for this now, but often on bigger continents with one of your first coastal cities you want to find an opportunity to sneak in building a work boat or two into the build queue a little bit after you get Writing and send them out exploring the coast. That coastal knowledge helps hook up trade networks, and sometimes lets you find AIs you haven't met yet. In this case you can kind of see that the northern coast is an icy dead end, but the southern coast you haven't even found Genghis Khan, who is presumably somewhere east of Ethiopia since the two are at war.
Tiwanaku is working an unimproved plainshill instead of running a scientist. Only do this if you are desperate for production (e.g., trying to rush out military units for an attack), not when you're slow-building a Forge. Since it has that barracks, it'd be nice to put that to use getting another couple military units for your attack. Also, the forge there doesn't do much - it's a city with trivial hammer production and you ought to have a bunch of happiness surplus from other sources pretty soon. Later in the game maybe when the city is pushing size 15 you might start thinking about that forge. Since you have a Barracks there, putting it on building military units won't hurt. When you're happy with your military and don't want more for a while, then maybe shift to a Forge in preparation for a potential military boom around Military Tradition research.
You don't need (or want) two farms on Thracian, especially since you got a lighthouse and it has a lake tile - that makes the lake tile 3F3C, which is better than the farm to work anyways (switch it now, your city governor is not). Speaking of the lighthouse by the way, you want to put a little thought into getting lighthouses and not just default to them. 60 hammers isn't a ton, but it could (for example) get one extra worker right now, which would generate more hammers on an ongoing basis, or a couple extra chariots to make your pending attack stronger, or most of the way to that library. Coastal cities with seafood resources they are working often want to get lighthouses early-ish, and Financial leaders with coastal cities that have the happy cap to work 2F3C coastal tiles generally want them eventually, but just put a bit of thought into it. It looks a little premature to me here. When you get Calendar that Bananas tile becomes a 5F plantation, at which point between that and the 3F lake tile you've got enough food surplus to live with for a while.
Why are there three workers stacked on a forest south of Cuzco? With rare exceptions, workers generally operate solo - you burned 3 worker-turns moving onto that tile where using just a single worker would have burned 1 worker-turn instead.
Cuzco is working an unimproved grass forest tile. It could be running a second scientist or stealing a hamlet tile from Machu Picchu, both of which would be better uses for its pop. Also that forest tile it's working should be chopped away and a cottage dropped on the spot. I notice from it's GP bar that you generated a Great Person earlier (presumably a Great Scientist); what did you do with him? I'm guessing bulbed Philosophy? That's a common move and not a terrible one, but if you have a good Bureaucracy capital you generally want your first Great Scientist dropping an Academy in the capital instead. When you get a second GS (20-40 turns from now) you might want to use him to kick off a Golden Age. Can talk about how to use that when the situation comes up.
Ollantaytambo needs a worker long since. It's working three unimproved tiles, and has a ton of choppable forests around it. The forge there is incredibly premature. Longer-term I'd probably build it for production, some mines on the hills and maybe daisy-chain farms 1N of Cuzco, 2N of Cuzco, 1E of Ollantaytambo so it can get a bit of food surplus where needed.
Macchu Pichu's borders are going to pop in 13 turns; you'll have Calendar by then, so be aware of it and ready to grab that Incense with a plantation. It's working an unimproved tile, about to grow onto a second unimproved tile, doesn't have a lot of production right now nor does it need happiness; the Forge is premature. A cottage by the river and a pair of plainshill mines maybe. That random farm the worker is building is better than nothing, but the city doesn't need more food; it needs something useful to do with the food it has.
Vilcas is on the right path. It's not a powerhouse city, just a spot that gives you some commerce and a bit of production while filling in your borders. Leaving one worker there is the right call, no urgency to faster improvements.
Huamanga doesn't need a Forge yet. It's 6/6 happiness right now, but as soon as it grows one size it will become one of your 5 largest cities and get +3 happy cap from Representation (making it 7/9). And as that whip anger fades, that will become 6/9, so it can grow up to size-9 profitably. I'm not sure when the border pop occurred, but the Ivory should be a priority as soon as that happens. Not only is it +1 happiness for your whole empire, which is nice, but it also unlocks building Elephants - excellent units to mix in with Catapults when going for a Construction-tech war. It's got the terrace, so no huge priority on production after that; I'd shift off the plainshill and be working that nice floodplains cottage you built to grow on it instead. You've got one more floodplains there to the west, so this city is headed towards something like 4x floodplains cottage, plainscow, ivory camp, wet corn, and a pair of plainshill mines at size-9. That's a powerful site. It'll have a whopping 11 food surplus from the floodplains and corn, so an alternative in Caste System would be to run something like 5 specialists, rapidly generate Great Scientists to bulb your way towards Liberalism.
I would prioritize Calendar ahead of Literature right now - the Banana tile is good, the Silk happiness would be useful, and in another dozen or so turns you'll have Incense to work. Monarchy for Wine happiness would be another useful one, although you might be able to pick up Priesthood in tech trade, conquer 3 cities from Ethiopia, extort Monarchy out of them in exchange for peace, then 10 turns later conquer their last city to save on the cost of researching it yourself. Longer-term you probably want to be thinking about how you want to win this game. The "classic" finishing move would be to work your way towards unlocking Cuirassiers, then just spam as many of them as possible out of your cities and conquer the whole continent with them. Upgrade to Cavalry if/when you hit Rifling. An alternative would be to play a more peaceful game and settle in for a space race win.
Some good trade options to get small edges. Don't stress about giving the AI a "favorable" deal. You could pick up around 100 gold and a couple techs for shopping Mathematics around. Trading with Genghis Khan will piss off Zara Yaqob and Washington, while trading with Zara Yaqob will piss off Genghis, due to worst enemy status. But realistically you're so far ahead in power that I don't know if you really care about that. You can probably get Monarchy in 2 turns of tech trading, which would let you improve that wine and add 1 happiness to your cities. Justinian will swap Clam for Cow. Doesn't cost you anything to do, go ahead and do it.
Military stack would be 1 turn closer to Aksum if it started 1W of Addis Ababa, rather than where it is now. That Chariot near Aksum could poke out and maybe get a look at his fourth city, which presumably is somewhere along that road southwest of Gondar.
You could give a shot at war with Ethiopia. I wouldn't trust a stack that small on higher difficulty, but I suspect it works against a Noble AI. Pick off his capital, follow on to Gondar if you can, reinforce a bit and go for whichever of his other cities is bigger. Then give him a temporary peace treaty in exchange for all the tech and gold you can extort out of him (you can always go back and mop up his one remaining city later). If you've continued to reinforce militarily, maybe with some war elephants and more catapults, and either Genghis or Justinian still lacks Feudalism, I'd carry straight on to take them out as well. Maybe even with Feudalism, depending on what your relative army sizes are looking like. When you generate 30 combat XP you'll get a Great General; almost invariably you want to use your first Great General to create a Great Medic - stick them alone on the same tile as a 2-move unit (like a chariot), combine them, then promote that unit with Combat I -> Medic I -> Medic II -> Medic III. Then you just keep that unit with your main stack and don't attack with it unless it's an absolute sure-fire success; it's there to heal the other units.