I would like to say a little something here, and I hope it gets well read, being on the 13th page and all.
This is coming from a person whose main character was created on a PVP server on the day vanilla WoW was released, so I hope that gives me at least some perspective on what I'm going to talk about.
This is a World PVP event, and the first experiment into cross-realming for events. Both of those facts should be kept well in mind by all attendees. This is not like trying to set up a well-balanced 10v10 premade WSG game. World PVP is messy. There's nothing fair about it: you gank, you get ganked, you get parties of people grouping up to find you. You call for help, you respond to calls for help... it's visceral, it's mean, and it's thrilling.
So don't be worried about whether or not there's going to be class balance among the two factions. Heck, don't even worry if there's the same number of people among the two factions. There's going to be absolutely no way to determine a winner or a loser... this is more for the experience of doing it, not for the bragging rights of winning. If you're going into this thinking you're going to be able to brag about your side winning afterwards, forget that notion right now and everyone will have a much better time.
You can bet there's going to be interference from higher levels. You can also bet that there's going to be protection from the higher levels too. You're going to die, a lot, and it's going to be frustrating if you haven't steeled yourself to that fact. Getting the most possible done despite those hardships, that's what world PVP is all about. Remember that this is a daily concern for people who are on PVP servers.
In my opinion we shouldn't have some neat, organized start time with two teams gathering up and saying "go". That's not world PVP. Log in, zone over, get to killing. If you are cross-realming in, I would strongly recommend that you work to secure your own P2P assistance in getting to AP. Rhae is a frickin' saint for organizing all of this, but I don't think it would be fair to stick her and a few other P2Ps on constant ferry duty and cause them to miss out on the fun.
If we want structured events with set goals, rules, and delimited playing fields, there will be time--and interest--for that down the road. This is more just to see what's possible and how the mechanics of cross-realming will work or not. Don't expect to be entertained... expect to be given the arena to make your own entertainment. This is free, open, bloody, smashmouth PVP. Run with it and have fun.
tl;dr: If I hear one person giving Rhae a hard time for anything that doesn't go perfectly, you'll be getting a chewing out from ME. And I'm good with words.