From what I understand german camo was often applied by hand with brush/broom etc. So would it not look more realistic to brush paint camo or can this be reproduced with an airbrush. If so how?

In my opinion, I think that it would be "correct" to brush the pattern over the dark yellow base if you were modeling a vehicle with a brushed on pattern. Remember, not every unit had the time, or access to spray guns. Pick a time period, unit, or battle and study what they did.

Above all, do your own thing, it's your money, time, and imagination....have a blast
(I have to keep reminding myself of this cause I want to run with the pros but have neither the time, skill, or resources)

John

Remember, during the later stages of the war, German camouflage started to be applied at the factory (3 color tan, green, red brown). Unit applied camouflage and markings depended on the materials available and the personal abilities of the crew. Most tank crews care for their tank much like an 18 year old kid with a Mustang, ride it hard but treat it nice.

Just check reference's & do a bit of research, if you are serious about
accuracy. Some camo was painted in the factory by spray gun and
also in the field by the Werkstattkompanie ( maintenance company ).
....What I do , if it was sprayed on like most Ambush Pattern's, then I'll
airbrush it - If by hand, then I'll brush it myself.
Like I said it just take's a little research to find how the German's applied
camo to specific/individual tanks.
- ralph