As far as the material goes, if there is lead rot starting, I would always advise giving it a brush-up with a treatment first (remember the bottom of the base). I use a 50/50 acetone and mineral oil blend. It can leave the surface greasy, so a quick scrub with warm soapy water might be needed to stop the paint sliding off. Those mins look fine and lead-rot free to me, although the fella 2nd from right might be close.
Other than that, nope, no issues and you paint them as normal. I do tend to go deeper with the shading to hide the imperfections in casting. There are sometimes some unattractive lumps and bumps lurking in the crevices.