To get to Xiahe from Xi-an you need to get an overnight train to Lanzhou and then drive for 7 hours. There doesn't seem to be any local transport to this area and you need permits to get there but there may be a local bus.
The train from Xi-an is comfortable but not as nice as the one that runs from Beijing to Xi-an. There are different classes (hard and soft sleeper) with the hard sleeper having 3 bunks on top of each other (6 to a compartment) and soft 2 (4 to a compartment). They do sell food and drink on the train but I'd recommend to bring your own snacks.
You can reach Xiahe by bus from Lanzhou and there must be a daily bus to Hezuo.
Further there not many possibilities for local transport.
In the Tibetan village we saw that the local people travelled by truck, in the back in the open air between the goods.