Farming

Build farms only when the planet nears its food pop limit and has good morale. The rule of thumb is one farm per entertainment building. Adjust for racial bonuses or wonders. One farm is plenty for average planets (6 to 9 initial tiles). Money planets with lots of farms, economic buildings and entertainment provide a real boost. Usually 15 tiles or more are desired to set up a money center planet. Of course if the map is poor, even small planets can provide some money.

It is a good idea to try to have approval at 100% for the first 20 turns or so with very low taxes. The extra pop from this will pay off big later in the game, and cost only a few credits early.

A player can use extra colony ships or transports to shuttle people around. It is a good idea to get each planet to one billion as fast as possible. Planets below this don't get full pop growth.

Should you? Yes. Population directly affects your income and your influence, and you want both of those numbers to be as high as possible.
When? Try to do it before the planet's population maxes out. The faster it grows, the better.

Up to a point.

For smaller planets, that point (for my playing style) is one Advanced Farm (10 mt of food production, giving the planet a total of 15mt). This size population can usually be kept happy with a single VR Center. A Stock Exchange also gives a small approval bonus.

If you want to grow a bit more without getting out of control, you'll have to micromanage building upgrades when you get new levels of farming. A population of 23 billion can be kept in line by about 4 VR Centers. This is with some bonuses for racial Morale ability, some trade goods like Ultra Spices, and maybe a Morale mining starbase. You can get to 23 billion population by building one advanced farm for 10mt and building another farm up to Intensive Farming for 8mt (which means stopping the upgrade to Advanced when you research that) plus the native 5mt for the planet. Fewer bonuses probably means adding 1 or two more VR Centers.

Once you hit 25 billion in population, you're in the approval toilet without a plunger. With racial bonuses maxed out, all relevant trade goods, and a Morale starbase, it will take at least 8 VR centers and sometimes as much as 10 to keep the planet's approval around 70 to 80% (depending on your tax rate). The good news is that once you pass 25, approval doesn't get any lower. Any population between 25 and 100 (the theoretical maximum, I've never gotten there) will have the same base approval rating.

Keep in mind that for a really high pop planet, you'll need at least 20 tiles' worth of VR Centers and Advanced Farms to make it worthwhile to pursue the max population. If you have room, may I suggest building your Econ capital and Political capital there, dismantle the starport, and if you still have factories left, build them over with Stock Exchanges.

don't sweat the population too much. you can easily build a monsterous economy with just 1 farm per planet. i strongly suggest you stick to '1 per planet' rule til you have a good grasp of the complexities of managing your morale.

another rule of thumb you can use is 1farm per 10 PQ(round up). understand, this is not a recommendation tho. 1per10 is workable, but not always smart.

oh, and dont bother with putting a farm on PQ5 and lower(6 is pretty iffy too) because you PQ population cap it too low for a farm to do any good.

Heh heh heh... or you could just mod the research buildings to make "genetically modified" food . Eg.

Lab level 1 - 1M food
Level 2 - 2M food
Level 3 - 3M food
Level 4 - 4-5M food
Invention Matrix and Discovery sphere can be something along the lines of 8 - 12M food.

The only drawback to this is that the lab buildings have a maintainance cost... But hey, you can build them on both the research bonus tiles and the food bonus tiles.

CAUTION !!!!!!!!!!!!!!!!!!!!!!

Putting a farm on a FarmBouns tile is a sure way to make a lot
of cranky citizens...

But, If you are lucky enuff to also have a morale bonus tile on the same
planet ...Build the EntertainCenter there, and it will balance the farm bonus.

Maybe avoid any farm upgrades after this is a good idea...

I consistantly dominate with minimal thought to high populations. On the times I bother at all I preplan what planet will be my breeding pit. Make it the one with the most Morale tiles. Put your economic and political capitals on it and fill up on Stock Exchanges. Economy starbases if you feel real frisky and your invasion breeding center is ready to roll. Pop out troop transports with 1 troop on them from your industry center and stack them outside the world. Siphon off troops to store for later use. Losing focus on your question. It all depends how you play.