No, thats a PST Gen 2 3-15. Carbine extension. Rifle started off as a complete Larue Grendel but I wasn't impressed with the accuracy so I had Craddock spin up a Bartlein barrel and replaced the BCG with the JP
Id spend the cash and get the complete JP BCG to go along with the bolt and SCS. I went through bunch of different gas blocks on my build. ended up sticking with the SLR. The XTR will suite you well, although its a bit large on a small frame AR.
NO, MILs is a measurement. Think about getting into the online training here on Snipershide. It will help you immensely. I also use the Strelok ballistic APP. this will help you understand bullet drop reference on specific reticles
MIL is easier to learn and master as its divided my tens. You can still use MOA if thats what you're comfortable with just makes sure the adjustments are in MOA. There are very good classes on scoped carbines
Close range is all relative on the task. In the woods hunting whitetail 50 yards isn't all that close. Hunting hogs, you could be taking shots (hopefully not defensive) well within 20 yards
for hunting it would work. It's not FFP and the German post Dot reticle doesn't have many features to help with range/wind. 56mm obj is also a bit much for a small frame AR. you'll have it mounted fairly high to clear that obj