Collapsing stock would be a benefit in fitment of the gun for the shooter. Vertical forearm grips would likely create one more thing to snag in brush IMO, and not needed for hunting. A good upper with rails would let you detach the grip for hunting use. 1:7" twist would be a must, heavy bullets of the correct type to hunt with, assuming like what was said, you would use 5.56mm. I know more people use it now than before, but it isn't my favorite big game caliber, and there is a smaller margin of error for shot placement IMO. I would suggest one of the larger calibers in the AR platform, and save the 5.56 for home defense. 16" would aid in making a compact carbine, while 20" would give you a little more velocity. Mags, of course use the legal mags for hunting, and make sure your choice of caliber is legal where you hunt. Also do note, that while I'm not going to judge you for using it to hunt with(it is just a semi auto rifle that looks mean,lol), antis, and fudds will be quick to point out anything you do is bad, including vertical forearm grip, etc.