Hi there!
Glad you're going to be challenging us! You are indeed in the right place, much of the Prime stuff is just still behind the scenes on here as of right now. Do keep an eye out on our [url=http://twitter.com/#!/PaxPokemonb8l]Twitter[/urlb8l], [url=http://www.facebook.com/pages/PAX-Pokemon-League/139432372766011b8l]Facebook[/urlb8l], [url=http://paxpokemonleague.com/b8l]the website[/urlb8l] and/or [url=http://forums.penny-arcade.com/discussion/139653/the-pax-pokemon-league-rules-are-now-posted/p1b8l]the thread on the PAX forums[/urlb8l] for news; a lot of stuff will be posted before PAX. (And some things, like the rules, are already on the site.)
Some gym leaders have different quirks for their gyms, including double battles and things like that, but not all of them.
Yes, the gym leaders and elite four will have bright green scarves to help in identifying them. (The E4 will have a red stripes or something additional to identify them as E4.) As you said, you need to defeat 8 gym leaders, then you can challenge the E4 and the champion. You don't need to have anything on you to identify you as a challenger, just ask for a battle. (We will also have special meet-ups where you may be able to find several gym leaders, but we also encourage you to find leaders at other times.) There will be more than 8 gym leaders, in the hope that you can find 8 of them throughout the weekend.
Good luck!