So long as the pokéballs are not damaged? They can spend a while inside of one, comfortably. Doesn't make the thought any easier, of course, and it's not something I would recommend anyone to do.

[Didn't make it any less concerning at all either. No matter how safe, the concern remained and... no want to further test the longevity of how long it would hold true.]

That many- and indeed. There are around one-thousand species of pokémon, perhaps a few over that number. There are new ones being discovered far more often than new types.