Hey Athithyan,
There are many places to visit in north-east
1)Sikkim- Gangtok,North Sikkim
2)Arunachal Pradesh — Tawang, Zero, Itanagar
3)Meghalaya — Shillong,Cherrapunji, Dawki
5)Assam -Guwahati, Kaziranga National Park, Majuli, Sivasagar
6)Nagaland- Mokokchung, Kohima, Mon
7)Tripura — Agartala
8)Mizoram -Aizwal
This is my itinerary of Darjeeling and Sikkim :
https://www.tripoto.com/trip/how-to-plan-for-darjeeling-and-sikkim-in-minimum-budget-5bacb0a591c80?ref=mobwapp&source=awp
Hope this helps.