It is a beautiful walk along the falls. I've been there in the spring, summer & fall, and the amount of water going over the falls was the same. There are plenty of signs that there is very heavy spring runoff, but I'm not sure it is possible to hike the trails at that time. In any case, I highly recommend the hike.
As to the hill between Red Rock & the park, no problem in just your vehicle, however I'd go in from the north if I was pulling a good size trailer or driving a RV. Not a lot of curves, just steep. I couldn't find an official grade for the road, but one review in
RV Parks Reviews states it is a 5 mile, 18% grade. The park info says it is 3.4 miles, but doesn't give a grade.