So, a day later I sat down again and looked quickly at the original, then started off drawing again. The result lacks the detail of number four, as I stopped the time at exactly ten minutes.
The arrangement of the heads is way better now, although some of the head turns are not satisfying yet - the general axi of the faces seem to point into the same direction (of the projection) except of the teachers. There is some sense of hands but I missed the hand of the man holding the paper and the hands of the man in the back and in the front. The body on the table is too short. I just realize that the teacher is actually sitting in a chair! The dark mass behind him seems to be the chair.
Just to add: this is the arrangement of the 8 people (not considering the body) as I think of it now