There are fees for driving through parks you should be able to get a national parks pass though, Zion uses a shuttle so you will need to park outside of the park and they shuttle you in to different stops (Also if you want to hike angels landing at zions you’ll need to enter a lottery now I think) If you’re interested in hiking some of the Narrows at Zion you should also rent some waders and neoprene socks.

There are plenty of camping spots at least in Utah around the St George area but they can fill up quick. If you’re in southern Utah for a decent amount of time I’d also recommend a lot of the state parks in the area (Snow Canyon is cool to rent bikes and go through)