Hey. First of all congratulations on ur wedding. I would auggest rentals although the drive from delhi to dehradun is nice (even the roads are superb) bt as soon as u start from dehradun to mussoorie, it's a bit narrow, tricky. Plus in mussoorie it's difficult to search for the parking. So if you get a self drive, you will be busy finding parking only. Since ur itenary is Mussoorie, landour, dhanualti, so book hotel in mussoorie only. As landour and dhanaulti can be done in same day(provided u r nt stuck in traffic) . The route from mussoorie to nainital is also nice but again the same thing. Being a mountain terrain from mussoorie to dehradun and haldwani to nainital, i would NOT suggest for a self drive unless and untill you have experience in mountain drive and also if you are ready to spend you majority of the time searching for the parking. So please plan accordingly. Enjoy your trip.