1. Nope, you can run full doors with the hard top. However, if you're looking to get a soft top, note there are a lot of parts required that don't come with the hard top. You'll need door surrounds, the frame & windshield bar, and a rear tailgate bar and side latches.
2. Used car, I would do the basic - plugs, oil, differential fluid, transmission flush, seafoam. I like to know that everything has been done and done right.
3. Hmm... this one I'm not positive about. Could just be a loose connection in the gauge cluster. Removal is simple. Pry up the long bezel running across the defrost. Unscrew three screws holding gauge cluster in at the top. Remove two screws underneath the steering wheel where that panel is. Remove two screws for the metal panel behind it. Remove two remaining gauge cluster screws and then pull outward. Put some degreaser on it.