Love that Lifecolor set.  8)

It's a personal choice really, I tend to assemble as much as possible in bare plastic to avoid glue marks in my paint etc. and paint the entire kit once assembled... tracks/tires are usually the only thing I leave off.

Others paint as they go.

If done correctly, the poly cap will allow you to spin the sprocket/tire on the axle, which will be very helpful if you choose to paint the teeth/tire after the kit is completely assembled.