Production cities are usually too limited by food and mines to grow too large, so size isn't such a big deal until replaceable parts.
If you're running food surpluses, just run scientists or other specialists, and you have no more growth problems.
Your capital (or other super science cities) and GP farm are the only cities where size is really important.
Mid game, you start with 4 health, hopefully you have +2-3 from forests/fresh water, you probably have a grain resource (+2 with granary), fish or animal resource (+1-2) and maybe a calendar resource. So that's 9-13 health, add an aqueduct if needed for 2 more. Most resource cities don't get that many grassland tiles.
Happiness, you can run hereditary rule, and get breaks from calendar resource, or drama, and occasionally gems with another 1 from a forge. Whales are hard to get, ivory and fur are usually mutually exclusive.
Furthermore, guilds is pretty out of the way tech-wise. On prince, you can easily mass swordsmen and a few catapults and grab a few cities before they get longbows.
Also, try beelining techs, and let the AI get the feudalism/theology etc. techs. You'll have alphabet for awhile so once you get civil service, trade code of laws for other stuff, repeat.
Thanks for the advice. There are a couple of things you mention that I already attempt to do. I generally chase Alphabet as soon as I have BW and AH, along with any of the "smaller" techs I need for developing resources (Hunting, Fishing, etc.). I generally rely on Warriors and Chariots for defence. If no Copper handy, I will research IW first before Alphabet. Next I trade for the religious techs, then go after Literature to build the GL, beeline COL to build Courthouses, CS, Construction, etc. to work my way up to Maces. Meanwhile building up Swords (or Praetorians), HA's, Cats and a few Spears (for defending my towns against AI Elephants and HA's). Depending on the situation, I then either target Paper & Philosophy on my way to Education & Liberalism, or Guilds, Banking, Nationalism, Gunpowder, Cavalry. I seldom bother with Archers or Trebs Naturally I look for trades along the way in order to grab Feudalism, Compass, Theology and the like from AI's (preferably from those lower in the points table, since they usually want to make a profit on these deals).
No matter how I try to plan things, my Capital usually ends up being my GP Farm/Science City. I do use the "Stop Growth" toggle on Production cities to try to control happiness & health in them. Since REXing always creates cash flow problems, I tend to build a Barracks & Stable in every city, so that they can produce troops, as well as a Market & Bank in every city, to try to keep the gold coming in. Obviously negotiate trade routes for spare resources.
I NEVER use GP's for a Golden Age. They either lighbulb techs, build their Academies, Shrines, etc. or join the city as Specialists. Engineers usually end up being used on Wonders, GM's get converted to gold.
I don't go after many Wonders. The GL as already mentioned, along with the Univ of Sankore if possible. If I have Stone, I sometimes try for the Pyramids (if I fail, the gold comes in handy for upgrading units; if I get it, I can switch to Representation early). Later in the game, the SofL, TG Dam and Eiffel Tower (although I have yet to reach that point in any game I have played past Noble level in the Warlords expansion).
These tactics have always served me well. To Monarch in the Vanilla and through to Noble in Warlords. But now (Prince) they consistently fail.