Quoted:
You already bought a carbine length gas tube, but the barrel you list is mid-length gas. Either you listed the wrong barrel or bought the wrong gas tube. Either way a gas tube is cheap.

Quoted:
You list a PRS stock and a carbine receiver extension kit.  The PRS uses rifle receiver extension, rifle buffer and rifle spring.

Why the PRS with a cheaper CMMG barrel?  Normally if your utilizing a PRS your looking for better accuracy than the CMMG barrel can provide.

Your spending a lot of money on the Black Rain BCG.  Why not get an AIM and allocate the extra hundred into higher quality parts elsewhere in the rifle?

That's a very tall bipod.  Most people are better served by 6-9" length or 9-12" length bipods.  Obviously that won't work if you want to shoot from a sitting position, but those heights are good for prone and bench shooting.  I've read good things about the new UTG Recon 360 bipods.  Several people have compared them to the ATLAS, you might want to check them out.

Is the Guntec rail free floated?  If you want accuracy I would recommend a floated rail.  I've got a few Chinese rails that aren't bad for about the same price.  Of course Chinese rails tend to be heavy.  Midwest Industries has a lot of good quality lightweight options but they're about $100 more.  I recommend a longer rail than 7", you can put a 12" rail on a carbine or mid gas gun, most free float rails have no problems going over a low profile gas block.

Quoted:
I prefer a 12" handguard because it lets you grip it farther forward for better comfort and control. It also lets you extend the front sight post out when shooting with iron sights which helps with precision.  Generally if my barrel is longer than 12" it gets a 12" or longer hand guard.  If it's shorter then I try to go with the longest hand guard that doesn't cover the barrel - which generally comes out to 1" shorter than the barrel length.