If you want an economic victory, you want to reach the Industrialization and Corporation techs first for the 5 gold per city per turn bonuses. That's obviously huge if you have a lot of cities. Get them both with 20 cities and that's 200 gold per turn for free on top of any other gold you're earning. This bonus is affected by Democracy and markets. So you want a bunch of cities, those techs and markets (buy them because they will pay you back quickly). You may consider Banks in your high-output cities but you don't really need them everywhere since you only have to get 20,000 gold.
If you don't want the economic victory, then markets aren't really needed. Get the free one for currency if you can, but other than that just the ind/corp bonuses will give you plenty of money for rushing units.
Generally the buildings in CivRev aren't that worth building. Yes, you do want markets for an econ victory, libraries for a tech victory and temples for a culture victory, but they aren't needed if not on your victory path. The general problem is that these buildings are 40 or 60 hammers while a settler is just 20 so you can always get more gold/science/production by founding a new city.
As for how to manage your capital, the main thing to keep in mind is that you should focus on one task at a time, especially in the early game. If you want to grow your city, then grow it. Most of the time you don't need to grow your cities much. Use Irrigation or a Humanitarian to grow all your cities. Growing one city isn't that big a deal. The exception is some Greek or Egyptian strategies that involve having a powerful capital. Much of the time when I play, my capital just stays at 2 population unless I get free growth. I usually use my capital for building units in the early game then whatever later on. Your capital is just a starting point and should be ideal for kick-starting your game. Its importance past the first 20 turns wanes considerably.
So if I grew my capital to 3, it would probably be because I wanted to build a settler before Code of Laws. It might be because I have three forests to work and want to be able to work all three or it might be because I have three sea tiles and want to work all three. A lot of the time I will just assign my citizens to work forests and I'm done for the game. Of course, I'm playing MP and those games tend to be fast, many ending in the ancient era. If I'm in for the long haul I will probably wind up growing someway, somehow.