Memorable experience. Try to visit during autumn when maple leaves turn red. There are some hotels in the hills, you have to ask smn in China to arrange sleepover there as they are not on booking. However you can do it once you've reached Huashan city (also there many unlisted hotels and locals renting rooms).
We went in June, a bit foggy (or smoggy) but still nice experience, worth visiting.
Grab some water, here small bottle cost 20rnb, fruits and snacks, but dont carry too much.
Go with t-shirt (there are like million stairs to climb so u'll get warm) but Dont forget a jacket as it may get colder in the evening.it was +35C in the city and +~20 in the mountains during day.
Avoid going during weekends or Chinese holiday: tooo crowdy. More