Kaziranga, Majuli, Tokolai Research Centre, Naimati Ghat, Gibbon Wildlife Sanctuary etc. You can check my Instagram handle https://instagram.com/round_a_world for recommendations
It's very much possible but depend on the weather conditions and snowfall conditions. Get in touch with voyage de mountains travel company for a better experience :)
Right now there is no quarantine but like Aditya said, there might be a lockdown here and there in the country soon. So, avoid for now. Even I was on the road for last 3 weeks and had to come back now coz you never know.