Definitely get a reservation for the campground. There are very few sites that will accommodate a large RV. I think that you could park at either Cliff and Balcony House and then ride your bike to see a lot of the ruins.
The park has a couple of ranger led bus tours which leave from Far View Lodge - very big parking lot. They're kind of expensive but look like they cover a lot.
http://www.visitmesaverde.com/frequently-asked-questions.aspx I have some more information on my blog -
http://rollinginarv-wheelchairtraveling.blogspot.com/2013/05/mesa-verde-national-park.html Have a good trip! It's a really cool place.