Those are a lot of questions.
Okay.
First:
You must chill! I have hidden your keys!
Costume wise: Stop stressin'. Focus on function and utility first. Pack a lot of loose billowy comfortable things, get dark, unvented goggles (and maybe some clear ones for night) that fit your face
before you leave town (snowboarders and GIs often have the best), pack a knapsack with canteen, a warm coat for the truly colder of the cold nights, & more socks and underwear than you'll ever need. Sunglasses. Hat. Work gloves. Your shoes or boots must be comfortable. Your baby wipes should be a refill size in a plastic bag, not a tub (which will dry out). Put the refill-sized wipes bag in a large ziploc zipper bag. Bring lemon juice to clean your dusty feet. And lotion. And sunscreen. And chapstick. And artificial tears. If you have room past that for costumes, add some silly hats or skirts or kilts or sarongs or something you've always wanted to wear. No matter what you wear, you'd have to work pretty hard ro be the weirdest @#$% there. There are costume camps to fill in the holes. It's gonna be fine.
Tents are sufficient. This will be my 7th year in a tent.
You don't want to be outcamped by a girly girl, do you? (That said, some people sleep in vans and box trucks and RVs, and I think the box trucks rule in particular--and that's what I would go with if I were a more confident driver.) My first four burns were in a cheapass, borrowed dome tent. It never blew away. Your mileage may vary. I do recommend Coleman 9 or 10 inch stakes instead of the measly six? inch stakes the cheapest dome tents come with. Also, get a tent with the least amount of mesh possible, sew the rest shut, and zip it ALL THE WAY. You might bring a broom in case the worst happens.
Ask your friends if they have a cot they're not using.
You need shade. And you probably need rebar for your shade; it's heavier than a tent. Google
simple shade eplaya for ideas. (Google anything with eplaya tacked on and you'll have a lot of great results). Top your rebar with pre-emptied soda bottles or tennis balls. Rebar injury is common, nasty, and mostly preventable.
No one besides me has ever entered my tent, to my knowledge. Unauthorized tent entry is not something that happens a whole lot. People are most likely to steal things that are left in the open: booze, tools, unlocked bikes (esp when drunk and tired, or mistaking it for their own), and occasionally generators. Put true valuables in your locked car. (Take your battery out of your laptop--if you must bring it.) Have a spare key. Wear one, hide the other. In 6 Burns the only thing that ever disappeared was my campmate's iPod from plain view in an unlocked van on Burn night. She's not even 100% sure it wasn't misplaced; she just couldn't find it and it's pretty likely.
There is not a higher degree of theft at the Burn than in the real world at all; it's just such a nice place that people let their guard down and are sometimes rudely surprised. People are also nicer at the Burn than in the default world, so any jerks you meet tend to stick out.
All right, it you have questions after this, read the Q&A Tips and Tricks forum and use that googling trick. I love to talk, but Radical Self-Reliance is one of the Burn's 10 Principles. You can do it.
