Gamera
Toshi: The Sharpie does work but I think I saw someone here complaining about 'bleed-though' and getting bad reactions with the paint. I won't use them again. I think your paint marker is probably much safer.
Gamera
A while back I mentioned about the use of the regular Sharpies and the reaction to model paints on another thread. Sharpie makes a separate line of oil based markers that are safe to use. Testor's paint pen is safe too. I'm sorry to say that the Sharpie ink will eventually burn thru your paint. It may take months but it may eventually happen.
There are many threads on this very subject so here is one of them:
http://cs.finescale.com/fsm/modeling_subjects/f/2/t/91035.aspx
Toshi
You are off to a good start.