With that said, is Wacken or Hamburg the best place to buy a tent/everything else needed? Are any other essentials available for rent at Wacken?
Wacken one version of almost anything you need at their campside shops (tents, chairs, sleeping bags...), But I don't know about quality/value for money.
I'm also bringing a somewhat expensive (mirrorless, not DSLR) camera and I'm pretty sure a festival is not the best place to leave it unattended, especially when I will be inebriated most of the time. Or does Wacken proper have these??
There's a truck with lockers to rent, if you bring your camera there right away it's save. Not sure which day it opens though, but the timetable will be put online several weeks before the festival.
Once one has said beer, I'm assuming most people use ice/coolers? In which case a bunch of those cheap styrofoam coolers are the best option?
Well, how you manage to get chilled drinks at your tent is up to your creativity! Some buy bags of ice in the village, some bring dry ice or dig holes in the ground that they fill with a mixture of salt and water. Others bring a generator and a fridge, some even pay local farmers to store them in their barn over the year. Others, like me, don't mind a warm JD Coke or Gin Tonic. For me it's part of the festival feeling.
Since I don't have a grill for cooking, am I at the mercy of whatever there is being served at vendors?
You can bring whatever you can carry. There are some (simple) vendors on the campground that are open from Monday, and on Wed the Wackinger market opens, which has really good food.
How "separated" is the campsite from...well, everything else? Is there any issue bring the beer one buys outside of the campsite into...everything else? If this is a strange question, what few festivals here in the US (sadly none are metal) you are locked into whatever vendors are selling inside the ticketed area and any outside drinks are prohibited.
The campsite is actually surrounded by several villages, two (Wacken and Gribohm) have supermarkets with everything, esp. drinks. still easily a good 45 min. walk, depending on where you are, so quite a challenge with drinks. However, since you come without care you will likely end up on campground A, which is close to Wacken. Bringing drinks to the campground is allowed, but no glass. Can't bring drinks onto the festival ground, except water. Campsite supermarket tents also sell canned beer and even rum, whiskey etc., to be refilled in plastic bottles.
I've read a few opinions in threads from the FAQ that frown upon getting there too early, seeing it as a burden to the organizers. To what extent is this true?
If you can, come on Monday. In my experience those who frown are those who can't.