I try to not tax more than 50% I also try to boost income from trade routes and economic improvements, etc. Planets 10+ I shoot for 10 billion, more on my manu. planets because of my troop transports. I don't try to go over 20 though because then I start running out of tiles, etc. and I don't like wasting my research on morale, farms, etc. Seems that with improvements in soldiering and orbital fleet managers, plus some decent ships, a planet of 10b holds it's own fairly well. At least long enough for me to get reinforcements over there.

Depending on my racial bonuses I'll lock taxes on either 59% or 69% and barely touch them for most of the game. With a 1 to 1 ratio of farms to entertainment this lets me maintain approval in the mid 50s. Most of my planets don't go over 15b, but I'll work to accommodate special tiles and get the odd planet with 20-30b or more on it. Late game my approval creeps up into the 60s or even 70s, at which point I'll consider raising taxes if it won't drop any worlds below 40% approval.

The advantage of low pop/high taxes is few tiles are taken up with it, and the rest can be spent on some sort of production. The disadvantage is that population is less disposable (yes, I play evil) and you have fewer troops if you are invaded.

It actually hadn't occured to me to try high population with low taxes yet, but the idea is interesting. With 59% taxes the morale penalty is 80% if I remember right, and with 69% taxes the morale penalty is 100%. When planning to run a low-tax empire you could ignore the morale racial trait and political party and go straight production. With low enough taxes you could probably use a 2:1 or even 3:1 ratio of farms to entertainment and create a few staggeringly huge econ worlds. The strategy would be strongly dependant on finding several worlds of class 10 or greater, and preferably a few of 15 or better. Planet Quality would be an important racial bonus to make the most of this strategy. I think I'm going to have to try it.

Does building farms increase your pop rate?

Ppopulation growth rate is not affected by farms.

I believe it is affected by approval rating (double if it's 100%)

i keep my taxes at 20% 26% and running on full production when you pop gets big anuff the money just rolls in. when im in debt becuase of war I crank that tax to 100 for a turn to get out of debt. you get a morale hit but by the next turn its back to normal, aslong as i dont time it too close to an election. helps me crank out thoughs transports with out worrying about population hit. if a planets moral is down i usually have anuff cash to drop a entertainment center on the planet to boost morale or buy a constructor