Marshall's made a "Pre-Color Spray", which put a matte finish on glossy/RC prints. I never liked it, as dust, pollen, etc. could settle on the print while drying, and you had to make sure the print was evenly sprayed. I had to use it a few times when I hand colored for other photographers, but always preferred a matte, or semi-matte surface.
Any oil paint will work. The paint is applied so thinly that it will be transparent. I usually recommend beginners start with a cheap set of oils. Until they get the technique down, it's a cheaper way to practice. Better quality paints will last longer, and won't discolor with time, but come at a higher price.