I don't know too much, but I'll try to help with what I know.
1) The camo pattern would depend on where it was positioned. If it was part of the Luftwaffe, it would remain overall Panzer Grey. If it was part of a mobile unit in the Wehrmacht, then they usually would paint it similar to the patterns on the tanks. The German High Command refused during WWII to standardize cammo patterns on armor, believing that non-standard camoflage would be more effective with a larger variety.
2) I believe that they had a crew of three to five personnell, someone can correct me if I'm wrong. They wrere: Crew Commander, Loader, Gunner, and one to two runners/alternate loaders.
3) They generally set up around the perimeter of airfiields, near Command Posts , supply depots, communications junctions (crossroads/railroad loading yards) and other military targets that were vulnerable from the air. Mobile units tended to be set up by Army, Divisional and Battalion headquarters and resupply areas.
4) In Russia, definitely! I'm not sure about the Western Front, but I'm pretty sure it happened there as well. Luftwaffe guns in fixed emplacements at airfields probably were if the gun crew commanders decided to whitewash them. Again, Camouflage was generally left to the discretion of company and sometimes unit commanders.
I hope this helps somewhat. I'm trying to remember my history from back when I built my flak 38 guns; it has been awhile. I'm sure others can probably revise or refine my information. I wish I had pics to post, but I haven't gotten that far yet.