Hi, I will be driving to Wacken and and want to set up my tent by my car. Do I have to - and thus how to do so - reserve a spot for my car and tent?
no, it's included in your ticket, so you can always camp and park your car. only if you're with groups bigger then 50 people you can reserve a special campground to be sure you can all camp together.
Just note you'll have to pay (I think 5) Euros for every day that you're early, because they don't want people to come before it starts.