Yep, that's how I do it

Depending on how accessible the upper run of track happens to be, I typically paint the road wheels, idlers, sprockets, return rollers and lower hull separately - just to make things easier. I'll then install the running gear and tracks, etc. I'll then paint/weather the track then touch-up the wheels as necessary.
On ocassion, I do build the entire model, then paint.
However, in the case of using individual track, sometimes I'll teporarily install the wheels then glue the track to them. When dry, I'll carefully remove the running gear and track as a unit, making painting and weathering even easier.
It's really half-a-dozen of one thing, and six of another!
As for primer, I ALWAYS prime - essentially because I use acrylics for my base coats. But, sme say priming is unnecessary, so it seems to be a matter of persoanl preference.

Mike