Also I didn't answer 1 or 2 because I'm not familiar with peepers. But:
1. I'd go with the larger one, tree frogs like to have space to climb.
2. If peepers are large enough to eat those crickets, yeah, probably after a generation or two raised in clean conditions the bugs might be less likely to have parasites. Those can be a problem in closed tanks where parasites build up in the environment and keep infecting the same frogs.