Just to answer another part ot your question: the towels they rent are pretty small. About the size of a hotel's bath towel. We were leery about bringing in out own towels because someone swiped our (actually our hotel's) towels there once. But we did borrow some old beach towels from a relative who lives in Orlando and they went unmolested for the last 2 waterpark visits of our stay.
Beatnik
PS We told our hotel what happened and they were pretty nice about it. Didn't charge us but asked us not to bring their towels to the waterparks from then on...