I would *absolutely* keep the current lighting and just add the fluorescent. If only because I can't see minor marring under fluorescent, only really awful stuff (by switching which lights I have on I can make a trashed vehicle look pretty good

).
Can't really help with which fluorescent bulbs to buy (still using whatever my builder installed), but I will strongly encourage you to buy as much light as you can possibly afford. Get long tubes and many of them. Too much is never enough. I have *dozens* of 8' tubes and I still wish I had more!
Two 4' tubes would hardly be worth wiring up and IMO four wouldn't be all that much better. I have some of those fixtures in-between my longer tubes and they really don't throw much light. Four 4' tubes is a so-so setup for a fairly small bathroom (we have one bath lit that way).
I'd put some 8' fixtures on the ceiling and some more on the walls. It'd be money well-spent in the long run.