thelsloot, two books to buy now are here-- http://www.phototripusa.com/E_Guidebooks.html
. I have the first and it's very useful. Buy them now to help you plan your trip. Use a search engine like Google to find van rentals. I would expect LV to have lots available.
One caution...it gets HOT, damned hot in fact, in the southwestern deserts in the summer. If your trip is around March thru May, I suggest visiting the desert locations early in that period rather than late. May is SUMMER is the deserts.
I hope you enjoy planning and taking your trip.