I wouldn't even consider going to a hotel during the festival. I got so fucked up every single night (to the point where I needed help getting to/into my tent) and it was so convenient and I felt extremely safe especially since I was 5 seconds away from passing out. I was also up at dawn every single day and people were always awake. The ground at Wacken is increadibly soft and it was actually more comfortable sleeping there than sleeping in any bed I've been in.
As for accommodation before/after the festival:
Before Wacken last year all of my friends stayed at a hotel in Billstedt (a little bit out from the CBD) called Panorama Inn Und Boardinghaus. It's 2 trains from the airport and all up it takes about 45 minutes to get there iirc. It's a 3 star hotel and the 4 star is right next door if you're feeling a bit snooty.
- Cold buffet breakfast (aka they have everything except bacon pretty much)
- Bar fridge (I kept my cold pack full of fruit and shelf-life milk in it before I took it to the festival and it stayed cold the whole time. Just an idea if you want to bring your own fresh food), TV, toilet, bath/shower, phone, desk, wardrobe
- Downstairs is a bistro bar called Einstein. I slept through the piss-up but I was told they have some sort of deal going on, I think it was 2 for 1 cocktails or something? They'll also feed you well
- There's an internet cafe downstairs from the 4 star hotel at a really cheap rate (for internet you have to pay for anyway). You can also make phone calls from there
- A stone's throw from the local shopping mall and corner stores, and a short walk from the train station
- The cleaners come in every day and actually clean it
- Hotel staff were increadibly helpful and friendly. They rang my room when my friend's phone wasn't working and when my mum emailed to see if I made it. They popped in to make sure everything was ok when I didn't leave my room at all after breakfast after the festival (as I was exhausted, alone and cbf doing anything), and there was always a warm smile and a polite "morgen" from all staff.
- If you get there before 2pm you still might be able to check-in, just ask.
The locals seemed all too willing to help me out with directions and so on, and I didn't even have to ask for it (I just had to stand there with a suitcase with a puzzled look on my face and they noticed)
So yeah hope this was helpful.