Regarding food i have given me a rule, never going below 500 000. And with coins, never go below 70 millions. If i am close to one of these i replenish first. It makes the upgrading very slow as with 10000 treats you get very little in level return.
Re treat farms, in fact the very large ones are useless, you only need 2 or 3 max to grow treats wheb you have money. The rest of them is only used for 3000 treats /24 hours. And for this, the medium farms are sufficient.