The campgrounds at the main park are usually pretty busy but the weather will probably make it easier to snag a campsite if you are so inclined. Springdale has more and more lodging opening up every month, but much of it is priced to account for the convenience of the location. There are lots of affordable hotels in St. George available and the drive is only about an hour.
There's plenty to see and do in the main park - Angel's Landing was closed due to a washout a few months ago and I'm not sure if it reopened yet. The Narrows are amazing, but will be very miserable at the current temps. That said, it's one of the most beautiful places in the world and just driving through the park is an experience.
I personally love Joe Braun's Zion website - he's super thorough and a great photographer - and has written a very good Zion Adventure Guide that should be available on Amazon.
My wife and I have spent a bit of time in the area, if you have some more specific questions HMU.