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.
If you love trekking then Kedarkantha is the best place for now trek is of moderate level.
If you want to chill in between mountains and take sip of tea in snow then you can go to Auli.
You can check out my timeline if you are going auli or you can send me message if you want to go for Kedarkantha as I'm also going for kedarkantha this friday.
South India is very huge where exactly are you planning ? Usually popular routes are to start from Kochi and Finish at Trivandrum, start from Kanyakumari and finish at Madurai after Rameshwaram.
काशी विश्वनाथमंदिर,कालभैरव मन्दिर,गंगाघाट,मणिकर्णिका घाट,सारनाथ,रामनगर किला,काशी हिंदू विश्वविद्यालय इत्यादि बहुत से जगह हैं बनारस में घूमने के लिए बनारस की सभ्यता बनारस का खानपान स्वाद बहुत कुछ है बस आपके पास समय होना चाहिए क्योंकि 1 या 2 दिन में आप पूरे बनारस का आनंद नही मिल सकता इसके लिए कम से कम 4 दिन का समय होना चाहिए ।
It is safe to travel Varanasi in January but carry a lot of warm clothes as the winter will be at peak during that time. Also, it will be good to go with a friend or family because you might face some thugs in Varanasi.
बस गर्म कपड़ों को रखिए और निकल जाइये बनारस घूमने बनारस सबसे सुरक्षित शहर है क्योंकि यहाँ देश-विदेश से लाखों पर्यटक आते रहते हैं इसलिए इस शहर में आपको हर प्रकार की सभी सुविधा मिल जाएगा।