You have a really good head start there, unfortunately this stuff is addictive, don't be suprised if the repainting of your helmet isn't the tip of the iceburg 
As for painting over rub-n-buf, I don't think it will take paint. It's a wax based material and the paint may just bead up. I've used chrome spray paints before, the silver on Boba's armor isn't all that shiney anyhow. If your seeking paint and colors, look up Rouge Studio's threads on proper paint and paint colors, he has them listed. The colors won't look right straight out of the jar, but are built up with layers of black mists to weather everything. Good luck 
