1

The driving is tight, but should be doable since you have a local driver.
A live sky burial may not be an everyday event. We waited 2 days for it. Ask the driver to check as soon as you get into Langmusi.

2

While at Xiahe, we enjoyed a short side trip to the Sangke Grasslands. Since it is a collection of tents grouped into two villages (Tibetan and Mongol), I can't say what the situation is in March. The meal we were served in the Tibetan tents (closest to the parking) was spectacular, including yak momo, yak yogurt, and a dish of lamb, onion, and crunchy peppers - the peppers are hollowed out, dried, and stuffed with a grain mixture and maybe sesame?

If you are talking about witnessing a sky burial, good luck. I am not sure the site itself is anything to see, but I didn't go. There is an outfit that does horseback rides in Langmu, and it looks like that would be impressive.

3

I've done one of the multi day horse trekking trips out of Langmusi, which was indeed fantastic, and a great way to stay with nomads. March is the time when getting into the TAR and Tibetan areas of Sichuan and Qinghai is the most difficult, so have back up plans. For the past few years the TAR has been completely closed to travelers during the month of March.