Its a good idea to paint the tank like you said, leaving off the smaller parts until you have applied the camo. For the base color you would want to use the dark yellow first then put on the green and red brown. If you want precise definition between the colors you may want to mask off the cammo pattern but remember that the crews on German tanks sprayed there own camo patterns with air brushes that came with the tanks. So a nice sharp line between the colors may not look right. I free hand the patterns on most of my German tank or trace it out with a pencil first.
The wash can be the same color over the whole model as well as the dry brushing. Or you can dry brush with lighter colors of each color, thats up to you. I dry brush with lighter shades of the base color on all my tanks and they look fine.
I hope this can help you out.
Good Luck,
Pat