I agree on the Maintenance issue. with Afforess.
I am playing a game currently, under SVN 878, because the updated SVN removes the A.I settled great Generals, ok I can accept that, BUT bump scrolling is painfully slow, and I won't accept that.
Running Republic
Anyway, on a Gigantic map, if I build another city, all my cities maintenance costs go up, If I build an Administration building they rise etc. that's all fine and dandy.
BUT just to throw a spanner in the discussion, I have 67 cities on my home continent, and 3 on the 2nd one.
I find, with running culture at a flat 30% I can run a 30% science slider, while building in all cities, that's a 60% Slider for the Math challanged. If I put the Majority on wealth generation, it hits 95% gross slider.
Now I could easily triple my cities, not a problem, I have plenty of space. But I've set up my empire, so its a HUGE CASH flow generator.
Like anything, there is a way around it. Size matters. I switched in a golden age to Republic, to test out costs, found I could handle them, and kept it going, its just gotten better and better cost wise, as I've grown cities.
So all civics are valid, Federation is probably the best cash wise for me, but

and

its easily Republic.
maybe I've mixed in the correct mixture of other civics, controlling 2 holy cities, and building ALL the Maintenance reducing buildings does go a long way.
I have trialed SVN 923, but bump scrolling, and Bug errors??? *SVN problems*, I won't continue, but maintenance is similar after update.