I went through doing a fancy Cerekote job on one of my AR's; it's expensive and like a body tattoo, difficult to revert if you don't like it later on down the line. My advice is not to do sophisticated patterns. I am in favor of solid colors for the furniture, reviver, and hand guards. If you do go down this path, rattle can spray paint has the advantage of being easy to apply and remove.
I painted my brothers AR as a gift. Not really to much to worry about. As another person here stated, just cover or lube up some of the holes. easier to clean up. My group used to spray paint out rifles as needed and based on the environment to be used. Never had a problem. Though understand you will get burn off or more correctly smoke off if you run a full mag or two quickly. Best to do it and get it over with prior to range day. The smoke off can be a little embarrassing.