Its a solid render sheets so anything you want, paint it, tile it etc. Masonry paint is perfectly fine. If its been up a while give it a good scrub over to get any dirt and growths off first
Best to seal up any screw holes, bit of ploy filer external. Personally I like farrow and ball, its pricey but gives a great finish. As with anything paint a small section and see if there is any reaction, if your board has a chalky finish when wiped with your hand.. seal the board. Sandtex sealer and paint are pretty good match.