Fly to Kolkata, and then to Paro, which offers some of the most spectacular aerial views of the Himalaya. From Paro, you must make forays to visit the famous Paro Taktsang or the Tiger’s Nest Monastery, where Guru Rinpoche is told to have brought Buddhism into Bhutan.
Drive to Thimphu, take in the Memorial Chorten, Buddha Point, and Changangkha Lhakhang. Also visit the Takin Preserve at upper Motithang. For stay in Paro, try Tiger’s Nest Resort, and Sonam Trophel Hotel (Tel: +957- 8-274444). In Thimphu, head to Hotel Norbuling or Druk Hotel Thimphu. For the Tawang leg of your plan, you could fly from Paro to Guwahati before driving up to Tawang, which is the easiest. Tawang is just across the Indo-Bhutan border but the lack of a good road and border formalities add something like 600kms to your route—which makes me question the bundling of Tawang with Bhutan for your holiday. For stay options in Tawang, try Hotel Siddhartha (Tel: +91- 9015878985) and Hotel Buddha (Tel: +91-9436872974).