Ok, couple of things...

First, a baby will last a looong time in a 25 gal tub. At least a year - maybe longer. My baby is about 4 months old and I won't upgrader her 20 gal long tank until next summer at the earliest. Baby's are more active than adults and they do like to climb, so make sure you have a nice branch in there for her to hang out on. Mine spends 80% of her time on her branch. She thinks she a macho ETB.....

Second, if you are going to be keeping her as just a pet, you probably won't have to worry about her reaching monstrous size. Keep her on rats all her life. If you move her to rabbits, it seems to trigger a lot of growth and she'll reach those monstrous lengths. She'll do fine on rats, even you feed 2-3 per feeding. Baby's will eat 1 rat pup per week (no more!) and then gradually increase as baby grows. My Peaches is still only eating 1/week. As adults, they usually only eat every 2-3 weeks. Don't power feed - they will reach the size mother nature intended them to be in the time they need to reach it. Rushing will only cause problems. Rats are good and will provider her with plenty of nutrition - if the rats are big enough and/or you feed 2-3 at a time, you will not be underfeeding. But the nice thing is that they don't seem to spark the same growth spurts as rabbits. You can NOT control how big your boa gets or how small she stays by what you feed - that could cause serious problems if you tried! BUT rabbits do seem to elicit an extra spurt of size that keeping them on rats seems to avoid.

If you are just wanting her as a pet, and keep her on rats, a 4x2x2 will do fine for her once she reaches adulthood. Genetics will play some role in the size she gets, so just observe her throughout her life. If she seems cramped, get her a bigger cage at that time.

And generally springtime is the time boas have their litters. I got Peaches in May at our local Rept Expo and they had TONS of baby boas there. I think generally May-June is the best time for a young baby. There may be some 2011's still available with breeders and you might also find some nice 2010's too. Litters can be born throughout the spring and summer though so if you're wanting a baby now, just call up some breeders and see what they still have. I got Peaches from Tim Koppenhofer at Special K Reptiles. He does still have both 2010's and 2011's available now. He was fantastic to work with!