I've got a YHM upper to go with it, but I'm debating on barrels, etc.

I'm thinking a 16" or 18" 1:7 CMMG medium contour barrel. Rifle-length gas system. Rifle-length railed forearm (I'm leaning towards a Daniels Defense Omega, as they are supposed to be narrower than most). PRI front sight/gas block. YHM Phantom flash suppressor, hopefully the one that's set up for QD with their suppressors. Optics....undecided, but I like that Millet DMR scope.

My hope is to make a relatively compact rifle that's not as unweildy as a full-size, yet still capable of shooting beyond 300m. I reckon I'll shoot mostly surplus 55gr FMJ.

So....thoughts?

congrats and nicely done. My new tack driver is on the way. I went 20". It is a Noveske rifle with the VIS. I have some really high expectations of myself and this rifle going forward.
Personally I like the idea of 18". Your rail choice seems solid. You are on the right track. Keep us up to date. Good luck.