Re: another newbie barrel?
By the time you get a barrel, gas tube, block, and f/f rifle length handguard all that's left is receiver, flashhider/brake, and bolt. So unless your factory barrel is wasted you may want to consider building a new upper, it'll run around $150 more than just changing barrels, but in the time it takes to push two pins and swap bolts you can have a different rifle.
Its your decision, I'm in a similar boat, I've decided to piece together a 18" upper to hold me over until I get another lower, then rebarrel my 16" which is getting rough to 14.5" with permanent fh. Vicious cycle these rifle will get you into. Lord help me if I ever get a registered lower.