Is there any shade to sit in if you don't rent a cabana?

Yes. There is benched seating near the children's pool and various little shady spots throughout the park. I suspect the seating will go quickly during busy times. Our family mostly just rented one of the lockers, which are also shaded, and just explored the park. We'd find shady spots here and there to stand under while we were planning our next water attraction.

There are also lounge chairs that are beneath one of the slides that provide lots of shade

Yes

Not sure but several responses to other questions indicate yes

There are cabanas that they rent out for $150 also. It’s shaded with chairs and tables but there are plenty of other beach chairs to sit in and relax.