Awesome to have more reenactors!
Anyway, what these guys said to you, pretty much cover everything. You just gotta show up to a event, check the unit out and how reenacting works out for you. If you like it, they will have more advice to tell you to start. All you gotta do is just to check it out.
Altough I can say most common advice is, when you are interested, get a canteen first. Sounds lame but its realllllllllllllllllllllllllllllllllllllllly handy and helpful.