Masquerades are typically where you perform a skit (sketch) or dance (typically not recommended for quality issues in the past) in your cosplay. There are also walk ons, which is where you don't do anything other than do a few in-character poses before leaving the stage. Unless your cosplay calls for it, then no, masks/face paint are not required. More often than not, they don't cost you anything outside of pre-registering early enough to get a spot. I believe that Masquerade is held on the first day, but varies between cons. Check the official con website/forums for the exact time and dates.
If you need ideas for a skit/dance/poses, then YouTube has a lot of awesome skits- go for the ones with about 1000+ views for good, great, and award winning skits, then anything under that for decent, bad, and horrible skits that you want to avoid.
Skyrim Casual: 30 % Done!
Kaylee Frye (Firefly): 40% Done!
Jem Carstairs, Oswin Oswald, Magnus Bane, Pikachu, Trainer White: Done!