I wouldn't even go anywhere near something like that. Not without a financial sponsor and risktaker. Especially not in germany. We not just only lack your typical next door racetrack, they are also fucking expensive.
A pricing range I could dig up for the Sachsenring:
- the track itself ca. 9-11k EUR
- paddocks ca. 1500 EUR
- small event hall ca. 1500 EUR
- technicians ca. 300 EUR, helpers (corner workers, etc) ca. 40 EUR, each of course
All of that is per day of course. There may be less expensive tracks, but there sure are more expensive ones too.
Plus from what I found you either need to or really want to have an ambulance standing by while racing is going on, which comes out of your pocket too. Plus you need a proper liability and property insurance unless you go and try to declare it something non-racy in order to basically rely on peoples individual insurance to cover it. I found an over 10 year old event of that liking by some more on the expensive side forum renting the Hockenheimring, and some digging around told me that it did cost them around 7-10k EUR for a single day, and they managed to get BMW as a sponsor for a pitcrew and shit, plus they declared it something consistancy-test-bullshit to at least skip the liability insurance for the participants. Add to that that your idea of a bigger race ala LeMons probably will fail as most tracks here have a limit to how many cars are allowed on track at the same time. Oh and don't get me started on cleaning fees if, no, when something fails and leaks...
tl,dr: If I'd be hired and paid to do something of that liking, I'd sink a lot of time and effort into it and make it happen. As a fun event? Wouldn't wanna touch it with a 10-feet-pole.