Well, I've been to Wacken, seen some pretty fuckin' heavy bands like Amon Amarth, Cannibal Corpse, Pig Destroyer, Misery Index, Napalm Death etc. I'm not really into black metal because some of the themes don't appeal to me and I can't stand any band that's into all that racial superiority bullshit, but I like my death, thrash and grindcore.
I started going to gigs about your age. I was kinda lucky because that was before hardcore and straight edge took off in Glasgow in a big way. If you fell in the pit, people would help you get up etc. Now it's all assholes doing kung fu kicks and swinging their elbows and fists around :-(
Alcohol is a big part of gigs. Personally, I don't get wasted at gigs because I wanna remember the night when I wake up in the morning and be able to stand up in the pit. I just have two or three pints spaced out over the night. I've only smoked weed before a gig twice and it was pretty cool. I know you said you're straight edge. My advice would be to reconsider it. My parents let me drink in moderation when I was a kid, like, a beer with my dinner or whatever, so I ended up being pretty sensible with alcohol and it's never done me any harm and I've had a lot of fun.
Some people take ear plugs to gigs. I don't because I've never had any problems other than my ears ringing afterwards, but remember that it's gonna be a LOT louder than anything you've ever played on your stereo.
Don't worry too much about your ancestry. My family is Scottish with Irish roots, but it doesn't stop my pillaging monasteries in my longboat!
And if you're going to Wacken, for fuck's sake take some sun block.