Hi Phil,
Yes, that's the plan -I think it's recommended it the kit instructions. I've resisted much rubbing down up until now, because I'm quite enjoying the novelty of a see through loco!
Once I've finished the basic bodyshell (I'm nearly there!) I plan to prime it to see if any further filling is required, then work on all the details before more priming and painting.
I'm not sure yet, but I might pause for a bit when the first phase is complete - there are several projects I put to one side to focus on the loco, which I possibly ought to get back to. Then I could detail the new body as opportunities arises me over the coming months, and put the old RH body back on the chassis in the meantime. Of course, all of my planning is pointless really, whatever happens will do so because it suits the mood that I happen to be in...
Cheers,
Andrew.