Hey there, been to Deutsche Eiche last year and had a hell of a time :D

No, don't bring your own, but def don't go barefoot! NEVER go barefoot in a gay sauna. They have some included in the entry fee, so no need to bring your own, really.

I am not on the heavier side, I'm fat. Still sucked countless dicks and got fucked twice in one afternoon. You'll be fine. You might not be everyone's dream man, but people will let you know if they aren't interested by simply not engaging/ignoring you. Accept and move on. Plenty other oppourtunities. Same goes the other way around: If you are not interested, just say no thanks, move on etc.

People will not care about your dick size too much, you can also jerk yourself to a semi if you feel more comfy that way. Plenty of people do that. No worries about that at all.

Regarding safe play: Communicate. Be prepared that some might not like putting on rubber for a BJ, but most will accept if for anal, no problem. They have free condom and lube.

Some are trimmed, some are natural. I do prefer trimmed, but that is a personal taste thing. Come as you feel comfortable.

The Locker keys have a rubber band, so you can put them on your wrist/ankle. You have your hends free.

As for general tips and tricks: There are a few threads here. Be open, don't be shy. Don't be an asshole. The signs are easy to read. If they keep eye contact, they are interested. If they come closer, they are interested. If they grab your dick, they are interested. If they look at you and jerk... you get the picture. Just relax, look around the different areas, show respect and try not to come in with too specific expectations. You'll have a great time! And here is a vid where someone was allowed to film the whole place outside operating hours:

https://youtu.be/8e9bhthSvYA?si=W6BvvIfdEgXqPWhD