Yes, you can. As an instance, you can find this question in the link below which was asked from a professional Kaplan teacher during a formal interview,
How long have you been teaching English? And how long have you been with Kaplan?
I assume the same is true about dancing, as Job Shadow describes his experience in dancing as,
I have been dancing/ performing since I was five years old
About your first question the difference I mean, present simple describes routines. So when you asks, "How long do you dance?", you might get an answer like, "I dance four hours a day." or the addressee might infer from your question his ability to keep dancing for a particular period of time, so might get this response, "I can dance for three hours, what have you got?" :)
One more point according to Top Notch 2 by Saslow and Ascher,
When describing continuing and unfinished action with for and since, the present perfect and the present perfect continuous are both correct. Some people feel the present perfect continuous emphasizes the continuing time a bit more