Here is the deal about farm:
A standard planet can sustain 5 bil people.
If you want to have more population you have to build farm (farm *only* increase the population cap)
Let's say you have a XENO Farm which if i'm not mistaken provide food for 6 milion people then 1 planet (whatever quality doesn't matter) with 1 Xeno Farm will have a max population of 5+6 = 11 milion people
If you plant 2 xeno farm you'll have 5+6+6 = 17 milion
As a rule of tumb each time you build a farm build also a morale boosting structure.
As for the 'food production' tile i haven't got the exact math behild but i guess if you have a planet (5 bil people max as usual) and you build a xeno farm on 100% food production you'll have 5+6+6 = 17 milion.
In general the more people you've on a planet the lower the morale will be (for that the need of the morale structure) , of course the more people you've the more taxes you'll gain so is up to you !
Generally especially on very high level planet is better not to increase population too much but to build economy structure.
Here are some layout you may work in for a class 10 planet with soil enrichment (11 tile usually) and the order in which to build them. (the first tile is the initial colony)
Industry planet
Factory -> you should rush build this one and set to social focus
Factory -> If you can rush this one too
Factory -> If you can rush this one too
Factory
Starport
Factory
Research
Farm
Morale
Economy
Research planet
Factory -> you should rush build this one and set to social focus
Factory -> If you can rush this one too
Factory -> If you can rush this one too
Starport
Research
Research
Research
Farm
Morale
Economy
High tax planet
Factory -> you should rush build this one and set to social focus
Factory -> If you can rush this one too
Factory -> If you can rush this one too
Starport
Research
Economy
Farm
Morale
Economy
Farm
Morale