Resin is closely related to regular plastic but It's a two part epoxy like product poured into a mold rather than bein injected under pressure into a mold. This alows for much finer detail and even for undercutting that tradional plastic does not. It does not respond to plastic cemetnt. You need to use either a CA super glue type product or two part epoxy. It is, however, more brittle than regular styrene.
As with any figures, they should be primed , light gray, tan or even white, work, to give your final paint better tooth to grab and to reveal mold marks and other defects. You can use any paint you'd use on plastics, and it can be applied the same as you would to any other surface, i.e., brush, rattle can or airbrush. Primer should be airbrushed or sprayed, however.
IIRC, vinyl mush be primed with an acrylic. Other paints won't adhere well.
A wash applies a very thinned paint/thinner mixture which will settle in the deepest recesses intensifying shadows. The ratio is about 9 parts thinner to one part paint. Black, burnt umber or other dark complimentary colors can be used. Apply it where you want to emphasize a shadow and not, IMHO< to the whole model. Enamels and oils work best.
Dry brushing is the opposite of a wash. A lightened color is applied to the high points/protrusion to emphasize the effect of light falling on the subject. Mix white or a complimentary lighter color with your base color. 25% lightener to the base color. Dab a wide brush in th emixture and wipe the paint off on a rag until almost nothing shows. Then lightly drag this across the model. Repeat with 50% and 75% mixtures of lightener to base. For extreme hignlights, a very, very light brushing of white on the highest points may be in order.