I'm pretty n00by as well, but there's nothing wrong with some fine grit (400-600) sandpaper and a can of krylon fusion (fusion is specifically designed to bond with plastic) camo flat black to make the gun look authentic. Considering metal receivers are hard to come by, and expensive when they do, this would be my choice. I've painted some of my wallhanger guns and they look good. As far field usage, that's a different story, the paint will eventually wear off, (but so will a metal receiver's) and its pretty easy to touch up or even give the whole gun a new paintjob with, you guessed it, a rattlecan.
hope this can help!