The best time to visit Udaipur is the winter season. The temperature remains comfortable and is apt for visiting the monuments and other places of interest in Udaipur. The best months to visit are September, October, November, December, February and March.
Many say if you need to book online you could if not you could go in person. There is thulabara booking and room booking. For darshan whichever hotel u plan to check in, ask them they will help you.
Udaipur is good to get the glimpse of Palaces, Lakes, Markets, Winter Special Food, Temples, etc all in one place. You can see the Wintage Car Museum, Cable Car Ride at Karni Mata Temple, Boat & Camel rides at Lake Pichola or Fatehsagar Lake, City Palace, Bagore ki Haveli with evening show, Sajjangarh palace on Hill, Neemuch Mata Temple, Morimagri Memorial, Hathipole Market, etc are some of places that you can visit.