Questions regarding RDCs (N scale) and Paint

[GreatLakesRailfan]

I just posted this on the Michigan Model Railroading board, but figured I'd post it here as well just in case anyone here that might have an answer doesn't read that board.

This isn't exactly a Michigan-specific question, although I have a free-lanced railroad that is supposed to be based in Michigan.

The question stems from a project I'm starting, specifically in that I want to repaint one (and later a second) Kato RDC car. I assume that there are a lot of good reasons why the real railroads, for the most part anyway, only painted the ends and left the sides free of paint ($$$, and probably why paint something that looks good enough without it?) but is there a reason why it would be unreasonable to paint an entire car? (Aside from cost of paint- although it sure is a lot cheaper in N scale than in 1:1 scale.)

Also, for anyone who can help, I know the motors were mounted under the floors of the cars, but the vent on the roof of the car was mainly an exhaust vent, correct? I found it rather odd that this wasn't part of the casting for the roof, but rather a separate piece altogether (leaving a somewhat oddly shaped recession with two "stacks" protruding from the roof).

And one additional question, kind of off topic, but...there is a type of paint I started buying from Passtime (Port Huron) over the summer that I haven't seen anywhere else that I can recall. It's not model railroad paint, but I've been using it because I like the colors they carry and it's pretty easy to clean up. It says 'Games Workshop' on the label, although the bottle has 'Citadel Colors' engraved in the plastic. I'm pretty sure it's stuff that the war gamers would use, but was wondering if anyone here would know where I could find this paint in the South Bend/Elkhart, IN/Niles, MI area?

Thanks a lot in advance for any help anyone can provide,

Charles Warczinsky