By high speed train from Xian to Huashan, do I need to online purchase the train ticket?

If you go there on the normal weekdays or weekends, you don’t need to buy it online in advance. If you will visit there in the legal holidays, then you’d better book the ticket online ahead of your schedule.
It will be cloudy in the most days of August and it will rain sometimes. The temperature will be 65F to 95F. If you will climb the mountains, a thin jacket is not enough for you. It will be quite cold on the top of the mountain. You are advised to take a warm winter jacket with you. Besides, you can also rent a long and warm coat in the scenic spot.
The ticket costing CNY180 is only the entrance fee of the scenic spot, which excludes the cable car services. Therefore, you need to purchase them respectively. Besides, the cable car of different routes may cost differently.

may i know how much is the cable cars cost for 2 ways?

As I know, the ticket including the entrance fee, a single cable car of west peak, a single cable car of north peak and express buses of two cable cars will cost CNY460/person.