I know others have answered but I wanted to give my own insight onto some of these, and for completeness I'm going to answer everything.
Volunteering
1) If you and three friends are all accepted as volunteers I believe you can expect to get a room together if you request that. But on the other hand I don't think there is a way to get non-volunteer friends in there. There is a limited supply of the rooms. You can also do part-time volunteering (no room) or full-time volunteering without a room (I believe you can receive another perk but I'm not sure if that's an official thing).
2) I believe they always need volunteers but it does vary by convention. Sometimes if they have extras they will bring you on for training (especially for things like DMing and coaching) where you shadow another volunteer. There is definitely a chance only some of you will be accepted. You could mention an "all or nothing" thing in the notes when you submit your application, and if you don't all get it you can withdraw your volunteer status right away. For smaller conventions FT volunteers pretty much work the whole time the dungeon is open (in my experience) so you'd all volunteer at roughly the same times. For GenCon they ask which shifts you prefer and on which days, so you could all make the same selections and have a good chance of it working out.
3) In my opinion you often times don't find out soon enough. For GenCon at least you know your status and schedule before event registration though. If you are a returning volunteer I think it is less of an issue, but for new GenCon volunteers I think you'd want a refundable backup housing option (e.g. if you can get something through the housing portal).
4) With a little care, as DM in the dungeon, you will only have one room spoiled for you. NPCs might see multiple rooms (like some did this year).
5) You definitely pick your preferences, but keep in mind that typically you'll be an assistant coach before being a coach, and typically a puzzle DM before being a combat DM.
Gameplay
1) I typically make small variations to my main build so that with an extra 10 tokens or so I can play any class with a decent build. But I also try to get into arranged runs on the forums so I know in advance which classes I'll be playing.
2) Not sure actually. But arriving early is the key to getting the class you want in a random group.
3) There is some debate on that, and it seems Hardcore was harder this year (from what I hear). Traditionally a solid Hardcore build would run you under $100, assuming good skill and teamwork. Perhaps now it is more. If you bought a single $1k token purchase from Jeff, which includes 4 Ultra Rares of your choice and at least one random Ultra Rare, I think you would easily be able to equip 2 or even 4 people for Hardcore. You would likely need to or want to trade unwanted stuff for wanted stuff and would have leftovers. Alternatively you could probably spend $200-$300 per character just buying stuff on the secondary market.
4) I hope INT, WIS, and CHA will matter more in the future, but for now DEX and STR are the big ones, with CON being good for extra HPs. Some people go glass cannon melee and max out on STR. Others prefer ranged and go DEX. Spellcasters go for spell damage plus DEX and CON to stay alive.
Treasure
1) Typically I suggest drawing your treasure because it is fun, but people will buy or trade for treasure draws. If they expire then their value will typically go down but somebody still might want them for collecting purposes.
2) I have horrible luck and my best two draws out of several thousand draws has been two Ultra Rares. But there are definitely high end things in there like Legendary tokens, Orbs of Dragonkind, 25K GP Bars, etc.
Tokens
1) I'm biased because I run TD Tavern, but I think tdtavern.com is a good source

There is a thread on the forums where people review trades. There is a forum section for individual trades, stores, etc. Feel free to reach out to me if you want a thumbs up on somebody you want to trade with or buy from. I can at least say if I've had positive transactions with them in the past. True Dungeon players are 99% awesome so you are generally fine, but there are at least a few bad apples out there (since we have counterfeit tokens).
2) There is a lot of trading going on at conventions. For example Wednesday before GenCon is a popular time. But most of it takes place online (websites, forums, eBay) throughout the year. The busy season starts just before Origins and runs through a few weeks after token development.
3) Completion tokens generally end up being more valuable than standard uncommons and rares from each year, but normally not extraordinarily so. I'd say the average completion token is worth 2-3 times the average non-completion token from the same year. There are exceptions. At one point the Ring of Heroism needed them for its recipe but I don't know if anything like that will happen again.
4) Silver Nuggets are great both for usability (more loot!) and future appreciation (they will probably only go up in value). Getting the first kilt (2017 PYP) means you can save up for the 4-kilt transmute in the future, but otherwise might not be something you want to use between now and then. It will likely appreciate in value as well. Neither is a bad choice.
5) About half of the rare tokens will one day be worth more than their trade good equivalent. A few may even be several times more valuable. But you never know for sure. Most uncommons and commons are pretty much just good to be converted into trade goods.
Misc
1) You have a small chance of getting a Golden Ticket in a $1k order which lets you do a special run at GenCon on Wednesday night. You also get a nice bag of loot. They typically can be purchased or sold for the $1,000 to $1,500 range.
2) That's a hard question. If you ignore everything else and just look at playing True Dungeon, I'd say skip the big ones and do PAX South and Gamehole Con. If 2018/2019 is a good indicator, you'll be able to play all three new dungeons each year at a lower cost and less craziness. At Origins there are more special events and tons of space, but also not too crazy or expensive, so perhaps that instead of one of the others if you prefer it. Or in fact going forward you could do Origins only if you don't mind waiting until the end of the season to see new content each year. GenCon is great in many ways, but it is also the most expensive and most busy place to play True Dungeon.