Yes, this is a IFA H6B and therefore your next point.
Last weekend I was on tour with "my" Avatar-H6B in the Erzgebirge (Germany, Saxony).
I have no information about which bus the puzzle picture is from. But it is probably not the one from the THÜSAC (different steering wheel, different arrangement of the instruments). It could be the H6B from Halle or Dresden. A wooden steering wheel was not a giveaway but a regular one, see the picture of "my" dashboard.