Answers in the order asked.

#1. The black uniforms were replaced almost immediately by olive colored tunics and trousers. Everyone wore the same uniform or parts there of. Keep in mind those are "tropical" overcoats. They were dark brown wool.

#2. Without a context for the photo there is no way to tell why these guys are up there.

#3.See #1. everyone wore the same basic tunic and trousers.

#4. I'm also thinking PaK 38.

the tank riders would carry 2000000 rounds of ammo each, 18 grenades, 1 MG 42 each, MG 34 for backup...Panzerfaust in left trouser leg, Panzershrek in other trouser leg, 40gal flame thrower , MP 40 , K98 , MP44 & A sling shot.
That's a PAK 38.