1. what is the recommended painting technique for wheels/sprockets etc i.e. on the sprue or when assembled?
2. regarding afv's, what is the general painting order of the whole thing?

antiTHANKScipation

Well, there are a number of recomended ways to paint wheels, personally, I don't like painting on the sprue. What I do is cut them off, assemble them then clean them up. I then stick them on a suitable stick (usually cocktail sticks) and spray them a darker color than the base color. I find plasticene really useful for holding them in place. after everything is dry, I then spray them with the base color. After that, rubber rims can be hand-painted using a very dark grey (never black) to simulate the rubber, these can then be highlighted and washed according to one's taste..... Jim

For wheels I always remove and paint them assembled. To many cleanup points and seam lines to do it on the sprue.

I assemble them and then (personally) I insert a round stick in the hole and hold the brush still and twist the wheel in the paint on the brush. I've heard of people using a rotary tool to do this. Do fast for me, I don't have a speed control.
When you get to AB time you can also make masks for a circle template from an office/art store. Make a mask out of tape and cover the center of the wheel.

Remove from spue and clean. Paint rubber Floquil Grimy black. Use a circle template to paint wheel. Assemble.
Tanks: Assemble hull, turret, cupolas. Paint each separately the base color. Assemble to paint camo patterns. Add wheels. Add tracks. Weather to your desire.
OPen top: Paint seats and set aside. Determine how much assembly any cannon/howitzer will need to allow for getting good coverage. Assemble and paint accordingly. Weather. Oaint interior surfaces. Remember, open yop vehicles genrally have exposed surfaces painted the same base color as the exterior, but camo patterns are not usullay carried over. Paint pther detial parts, radios, shells, etc. Assemble the interior. Do you final; assembly. Paint the exterior. Either gently mask the interior with loosely packed tissue or aim your airbrush away from the edges to avoid overspray. Add wheels then tracks. Weather to your taste.

Paint maincolor on wheels when on sprue, then when removing and sandpapering I paint the usually black rubber on the wheels