Woah! 3 pages...awesome!
I'll update the OP, as well as address a few questions here:
What if I'm late?
Being late is just fine! The map is not instanced; as soon as you get in you can meet up with us at any time. I plan to be in for at least 3 hours, others may stay later, leaving earlier is of course fine as well. Just please try to have TS installed and tested (IE: you've at least connected to cgalliance) beforehand, if you haven't already, so that no one has to walk through that then.
Traits/suggested builds?
Already answered a bit, and I'll touch on it too. First, bring whatever you have - no worries if you don't have a perfect WvW build, or are missing slots. If you are made of meat, and can act as a shield, you can help.

In WvW you can expect to see anything from small skirmish to large 60+ person battles. Generally people tend to spec ranged, and AoE. This is both due to the number of people, and the usual frame rate drop. The other nice thing about AoE is it lets you assist with more kills, gaining you much more XP. Since we'll be with a medium-sized group, we can roll over anything small, so plan for big.

Also
strongly recommended to have a speed boost. Mobility is very important - getting back to the fight after death, chasing down a fleeing enemy, or running from one yourself.
I will post my guardian build today or tomorrow. I run staff for the line of warding, might buff, aoe heals, aoe auto-attack, and swiftness ward. Ward is great because you can hit more than 5 people and cast it in front of yourself while running to get the whole group moving. Typical utility is Signet of Resolve, Save Yourselves!, Hold the Line!, Wall of Reflection, and Renewed Focus.
I'll start a 2nd thread on WvW builds. I know others can speak specifically to Thief and Necromancer. Edit to add: I'd definitely recommend against minions. Excessive AoE will burn through them. I'd lean more towards wards/lifesteal/etc.
XP/loot/etc
Just to clarify what is above, getting the "same amount" means you are getting the same percentage of a level. So you will level just as fast at level 70 as you do at level 10. Actually it's probably faster since you'll probably be better at your class by then...and especially compared to general PvE.
You will get tons of level-appropriate blue/green/and even occasional yellow drop from kills. This includes killing enemy players; the game generates loot just like it does in PvE. You can also get tons of high level crafting material, like orichalcum, assuming you are high enough level to use the correct tool. Plan on bringing the best tools you can equip. Lastly, you get siege plans for WvW and badges of honor, which can be traded in to get more siege weapons, craft legendaries (have fun with that), or get level 80 exotic weapons/armor.
Also, I got more karma in 2 days of WvW than I did from leveling 1-60.
Lastly...remember there's no such thing as a dumb question - ask away and we'll all get better.