This is the case in GC3. Having a lower approval results in direct penalties to population growth, raw production, and influence, all the way to -25%, while having 100% approval results in a 25% bonus. In 1.1, this is properly reflected in the tooltips/UI.
The -25% growth penalty from 0% approval barely matters. If I'm not mistaken, the approval growth modifier stacks additively with the other growth modifiers rather than multiplicatively, and the each of the other growth modifiers is at least comparable in magnitude to the approval growth modifier.
Yes, roughly half your buildings should be farms, with the assumption each food building provides 6 pop and each production building provides 100% (adj bonuses are averaged into this). Changing averages doesnt change the results much, but might on lower class worlds. regardless, I would still shoot for this target. Again, this is only with 1.1, not 1.03.
What the balance 'should' be depends on whether or not you're playing in a way that makes you need approval structures to help support the additional farms. If you can ensure that the approval rating does not change, or does not change significantly enough to warrant the construction of additional morale structures, regardless of the number of farms you built on the planet, then yes, building a farm for each factory, lab, or market is a reasonable balance. If you need to build some number of morale structures for each additional farm, the balance shifts away from a 1:1 ratio and favors building more factories, labs, and markets.
There is also a question of the length of time required for each additional farm to begin paying off. Factories, labs, and markets all begin to provide benefits immediately upon completion, and moreover do not have a build-up period to reach their maximum benefit for the current population. Farms, however, will provide no benefit until the current population exceeds the population which would have been the maximum population without the farm and furthermore have a build-up period to reach their maximum benefit for the current output multiplier.