You already got some great answers from people who know what they are talking about, but since I hope you will try out Grind, and since I'm one of the DMs and can give something close to official answers, I will reply as well.
1) You get only one treasure draw and a completion token (which is usually unique to Grind). You can equip treasure-enhancers but they have no effect.
2) My favorite Grind run may still be my first one when I didn't have any idea what to expect. Certainly it doesn't hurt to try it once, and if you like more of a challenge and more roleplaying than you get in the regular runs then I'm sure you'll love it.
3) Normally True Grind runs sell out the quickest so I am very surprised there are still any tickets available. Perhaps it is because Jeff forgot to put "True Grind" in the title of the events. But I fully expect it to be sold out before GenCon. If not, we will run it for whoever is there no problem.
4) Yes, like the normal dungeon you all have to agree on a difficulty level, with Normal being the fallback. Note that Normal is still fairly challenging, about the same as Hardcore in the dungeon, but lots more combat too. There is no non-lethal in TrueGrind (as Eric likes to put it, the only non-lethal option is for the monsters if you so choose).
5) If you have a 6:01 dungeon run, you'll be in the epilogue area right at about 8pm sharp. If you ask nicely you may be able to grab your loot, save your treasure draws for later, and make it to the grind coaching room by 8:05PM or so. That's cutting it close for an 8pm Grind but not impossible. If you find your party on the forums beforehand (so you can figure out your class and let them know you'll be a bit late) and/or have your character pre-built (e.g. printed out or in a mobile app) then I think it will work. Ideally you'd have builds ready for a few characters in case your first choice isn't available by the time you show up.
My online token shop:
www.tdtavern.com
We buy, sell, and trade True Dungeon tokens. We also have a convenient consignment program where you can sell your own tokens.