If you need mostly adult mice to feed your snakes, I would get rats instead. It takes alot less time to grow up rat pups up to the equivilent size and weight of adult mice than growing mice up. I used to do mice at first for my corn snake but when he grew large enough to take young rats, I decided, once I got rid of all the mice to use rats instead. I originally had two colonies of mice, 1:4 and 1:5, produced anywhere from 30-50 babies per tube with most of my mice having about 10 babies on average. SOme will be a couple more, some a couple less but 10 was a good average. The largest litter of mice I had was 14 I think. Anyway, but the time these are weaned and are separated into a large grow up tank at 4-5 weeks of age and grow to adult size in another 3-4 weeks, I could have two batches of rats reaching the right size.
The excess food I sold off to another snake keeper in the area so that help recover the cost of feeding and housing all these mice. However with Rats, I don't need to keep the babies as long and rats don't smell at all as bad as mice, even when using vanilla in the water.