The museum is a little off the main areas but otherwise here is the bus schedule to Nanning:https://imgur.com/a/Ojnh1bj
You can tell if it goes to the east (Langdong) coach station by the longer distance, and although they are not as frequent it would be easier to stay near the east of town for the train station, however everything is connected well with the metro. If you have to go to the South station it takes maybe 45 minutes to the other one. In the middle of town, Chaoyang Road, you might find it more "fun" in the evening.
Depending what you do at Huashan you may have difficulty finding transportation to the coach station. It should never cost more than 30, and print out 宁明客运站 for the coach station to show a driver. They might also understand "bus" of course. I saw a bus but unclear where it actually stopped. Oh, and from the train station it should only be 20 RMB.