> If everyone went veg, we would need more farms right?
No, cows eat too. Think about it this way: to get 1000 calories worth of energy from a cow, that cow has to consume more than 1000 calories due to maintenance (BMR) alone. Moreover, one acre of land producing soybeans, rice, or legumes much more protein and much more calories per year: https://en.wikipedia.org/wiki/Edible_protein_per_unit_area_o...
> How many more field mice/rabbits/snakes/whatever will suffer/get squashed from this?
Fewer as shown from the previous point proving that we could feed more people on less acreage of land
> Is this number comparable to the amount of cows that suffer for steak?
No, it's smaller and we get to cut out the cool parts like raping cows to produce milk and then ripping their children away from them.