Hey, those are good news, props ! Good idea with the merchants.
Also, yes, the eco screen, F2, is very useful to check where your money is going/coming from.
My advice : complete the game at the easiest. So go for Domination. It will save you a lot of time and make use of the overwhelming army you already have - no use having an army if it stands still. You can always start a new game if you feel the urge...
You can raise your science slider at the moment : reach Steel first, then you can lower it if you want and get some upgrades.
Mansa is likely to capitulate after you capture 1 or 2 cities, so the game is well in hand.
For the future : try and work on your economy earlier.
First phase is always expansion (so, do not cottage when you have a single city). Then, from 3-6 cities, if the game is peaceful, economy is the focus : growth and cottage non specials. Then keep expanding, by whatever means is necessary.
Your city placement is ok, so you shouldn't have any trouble improving that part of your game.
Get some infrastructure, especially in your capital. Get Libraries in most places if you do not have anything better to build (better builds : settlers, workers). If I'm not warring, I will routinely build 5+ libraries between Writing and, say, Civil Service (random example).
If you wanna try a space race, Oxford University is a crucial build. You should try to complete it around or before 1000 AD. Means libraries, means universities, probably means using a Great scientist to bulb into Education. Having invaded and killed an AI before that point would be nice.
Lastly : some more attention on your civics and great persons will pay off big time. (not just Slavery : Bureaucracy or Organized Religion are huge eco boosts.)
ps : you can also install the BUG mod (unaltered gameplay) if you want a more user friendly interface (a bar for
points is a good reminder that you should produce some...).
BAT mod is another option (unaltered gp as well) but the "improved graphics" are not for everyone's taste. I think forests and jungles look too alike.