Trashigang is one of the biggest districts which is also densely populated. There is a different ethnic group under Trashigang such as Brokpas at Merak and Sakteng, who have totally different cultures and traditions and also have their own dialects. But the majority of people speak Tshangla Lo (Sharchopkha).
On the western side the valleys are broad and people settle at valleys, but on the eastern side, we do have V-Shape valley, so generally people settle on the mountain side, not in valleys.
If you want to make your trip short you can directly fly from Paro to Yongphula which is just one hour plus drive from Trahigang.