A couple months back I got a free 0.1 normal ball. When I went there to pick her up he had her in a 40 gal. aquarium. He said if I wanted it he would take $50. It was only a year old plus came with a water dish a couple hides and vines. It was all fancy stuff and looked nice so I said hell yeah. Well after two weeks I realized they was no way I could keep the humidity up high enough for a ball. So I took her out and put my biggest corn snake in there (over 5 ft long) Well as I am typing this he is shedding. The worst shed I have ever witnessed by any of my snakes. I spray the tank daily, but northern WI winters are very dry. So he will go into a tub once again. Now to the point, I am thinking about throwing mice in there. How big of a colony could I put in there without having issues with the mice.

A 40 gallon? What's the floor size? I keep 1.3 or 1.4 in a 10 gallon with no problems. You could probably keep 2.10 in a 40.

A 40 breeder is 36X18, but off the top of my head not sure the footprint of a 40 long..

If you want to keep the tank for the snakes you can put a humid hide box in there to take care of the sedding issues. Make sure to put the hole in the side of the hide and not the top. I like to use spagnum boxes for all of my snakes.