This is one of the most beautiful places I have ever visited. I was there on a weekday in April, and there were crowds but not excessive crowding. Highly recommended! This is a great addition to a trip if you are visiting the Xi'an area.
I was on a tour, which saved a lot of hassle trying to figure out tickets, but it means I can't give any practical tips on how to navigate all the ticketing, etc. However, many reviewers seem to have done it on their own, so apparently it can be done. There is English-language signage and maps on the mountain, but I didn't see any in the visitor centre.
Some of the trails might be a bit frightening for people who have a fear of heights, but the main trails are all safe, at least when the weather is dry - but wear footwear with good grip in any case. In the rain it might be questionable, as there are a lot of stairs cut into stone.