"I thought it's allowed to stop to take photos, a friend told me that he found a bus with all the tourist walking in a circuit corner"
Your friend was exaggerating. You need to be aware of the rules which apply at the 'Ring. It is a one-way public toll road with over 70 corners, featuring blind crests and fast, technical corners. You need to do at least 50 laps just to learn where the track goes BEFORE you can think about going fast. It is not a racetrack as such now, altho' it used to be the venue for F1 and bike GP races!
The German driving laws apply to the 'Ring just as they do to the roads around it, and they are now strictly enforced. Anyone found 'stopping to take photos' is almost certain to be reported and prosecuted for putting other drivers' lives at risk, not to mention their own. If I sound negative, it is because stupid driving and poor overtaking cause a lot of accidents there, especially at the weekends when the track is crowded.
"There is some kind of bar/restaurant very near racetrack, and some bridge"
I think you are referring to Breidscheid, an exit/entrance about 6 miles in, which has a great viewing area above a double apex left-hander.
"I will for sure prepare a onboard camera to record the moment"
The company which owns and operates the 'Ring banned the use of video and still cameras several years ago, seemingly because it did not want the negative publicity of crash scenes being posted all over the web and the press. If a marshal spots your recording equipment you will be banned from using the 'Ring and your gear will be confiscated.
It is a unique place, but it demands total respect and concentration, especially when riding a bike there.....
08 CBR 1000RR Blade