So I was hoping to find more information on maintenance costs and happiness over on the civ fanatics forum but it seems to be hammered right now (big surprise).
Here is a list I found out for unit maintenance costs:
16 / 102 (+14)
15 / 88
14 / 88 (+14)
13 / 74
12 / 74 (+14)
11 / 60
10 / 60 (+13)
9 / 47
8 / 47 (+13)
7 / 34
6 / 34 (+13)
5 / 21
4 / 21 (12)
3 / 9
2 /9 (+9)
1 / 0
0 / 0
This is from the modern era. It looks like every 2 units causes a big jump in costs, with the jump table increasing based on era. Unit count includes workers, so get rid of stuff you don’t need.
It also looks like the formula for happiness is 2 per city and 1 per population. This means that India “breaks even” on happiness at a city population of 6. Anything above 6 they start to get a bonus. From this I should be able to figure out what buildings are required to make a self sustained city, aka what buildings offset the unhappiness, how much do they cost, and how much would that city have to pull in to make up for the gold costs.
I really really wish there was a screen that would tell you upkeep and income per city. Also, you should be able to destroy buildings, which it does not appear that you can.