Yes, you need to start from Guwahati and u will need maximum 6 days to complete Tawang trip. 1 night Bomdila, 1 night Dirang, 2 to 3 nights Tawang, 1 night bhalukpong.
If need any further details I can assist.
Depending on your preference, you can reach Tawang by air, railways or road. You can take a flight to Lokpriya Gopinath Bordoloi International Airport in Guwahati, which is located at a distance of 480 km from Tawang. From there, you have to change the bus 3 times. Choose APSRTC bus service. First, take a bus to Tezpur. From Tezpur, take a bus to Bomdila. And from Bomdila, take the final bus to Tawang. It is suggested to stay overnight at each place and travel in daylight. You can also choose to take a flight or travel via train to Tezpur, and from there, continue your bus journeys.