I would recommend contacting the manufacture.
A standard Mil-Spec tube will work.
Yes, the trigger guard is not detachable as it is part of the molded plastic of the grip.
This version is not. Daniel Defense does have an MLOK version sold alone, but this kit is made for Picatinny style rail.
You can simply get an MLOK to Picatinny rail section adapter that hooks to your MLOK rail and allows you to put Picatinny attachments onto that.
Please email us at techsales@opticsplanet.com so we can further answer your question.
It is meant specifically for a mil-spec buffer tube.
If you are asking about the vertical foregrip, it is picatinny.
This stock is a mil-spec sized stock and will fit ANY mil-spec receiver extension.
Yes, this is a multi-position carbine stock.
Unfortunately we only sell the MLOK vertical grip separately, we do not have it in a kit. This set will fit on a Ruger AR-556 provided you have a quad rail replacement drop-in handguard, or have the MLOK version with a rail section added.