A few questions in there
There are a couple of basic approaches people are using to mark metal (a 40W CO2 laser can’t really etch anything except the anodization of aluminum).
The first is a material like Cermark or Thermark. You spray a coating on the metal and then laser (use an engrave setting). This fuses the material to the metal very similar to the way laser printers fuse toner to a piece of paper. This creates a very tough and mostly permanent black (or other colors with Cermark) engraving on the metal. It looks like all those steel water tumblers with various graphics you can buy in a store. The spray coating that was not lasered washes off.
Dry Moly Lube is an alternative to the products above. It’s about $11 vs $100 a can and is available in your local autoparts store. It doesn’t leave quite as black a design as Cer/Thermark but it is certainly good for many applications. You’d have to decide for yourself though if it fits what you’re trying to do.
The other major approach to getting a lasered design on a metal object is to use paint. You can paint first and everything you engrave will expose the metal. Or you can mask the metal with a vinyl transfer tape (it’s not really vinyl btw so it’s safe in the laser) and after the design lasers off the masking, you paint the piece, let it dry and then peel off the remaining masking.
Either approach is safe for your laser. Acrylics or other paints can be used in either case. It would be a rare paint that you couldn’t laser - certainly not any of the ones you’ll find in craft and home stores. Those should all be fine. They will tend not to be as tough and long lasting as Cer/Thermark but may well be all you need - you could experiment with some paints to see what their wear characteristics are. For art pieces paint would be fine as there’s not a lot of handling. On the other hand, a keychain might expose the paint to so much wear that it abrades off over time.
So your decision is really around what you would like the result to be - marking on bare metal (Cer/Thermark or masking then painting) or metal showing through a color layer (paint before lasering).