Are you working with a trainer? Or know anyone who shows where you are? Schooling shows are different in different parts of the country so I'd try to find out what's considered normal at the shows by you. The schooling shows around here are on the more formal side. People wear either 1) Tall boots, breeches, show shirt, jacket, gloves. Or if you're young enough 2) paddock boots, garters, jodhpurs, show shirt, jacket, gloves. Some shows are casual enough to allow half chaps, some aren't. Some shows expect braids, some don't. Some allow polo shirts instead of shirts/jackets but definitely not here!
As far as the medal class goes, this would be another place to ask a trainer! Depends on the medal class. Some medal classes run like a classics class: you go in for your first round, they announce your score. Then you go in for your second round, they announce your score. They take your average of the two and that's how they ribbon everyone. Most medal classes though, everyone has their first round. The judge calls back the top 6 or so riders for a "ride off". Generally the ride off is more complicated then then the first ride. Maybe the judge will ask you to halt on course, trot a fence, add an extra stride in a line, do a bending line or roll back. Although I've been in some that were as simple as a stirrupless posting trot.