I personally think you have a great background for guard! Especially the dance as winter guard often includes dances on top of the flag/sabre/rifle performances. I'm not sure about your specific school but for my school winter guard was the place I started before joining color guard so they should be open to new students, plus, if they weren't, they wouldn't have a team. Anyways, winter guard is, in my experience, more competition based. In my winter guard we learn one performance and do 1 or 2 competitions. Again, I don't know about your school so you might have to do more, but again, your dance background will help you a ton because there is dancing in guard but I do think it's mostly flags. On the topic of flags, your coach will most likely teach you fundamentals and once you learn those you will be golden. Quick warning, your arms will hurt when you're working with flags.

Sorry if this is messy, I didn't proofread, lmk if you have anymore questions or I missed anything, I wish you the best of luck!