It will come with two accessory rails.
Tacfire lists the 12" handguards as 13.3 oz.
Yes, it will come a proprietary barrel nut.
Yes, it will come a proprietary barrel nut.
Yes, as long as its an AR15 (.223/5.56) but please be aware that these are not drop in handguards. These will fit any mil-spec AR-15 upper receiver.
No, a list of compatible handguard models for the Pantheon Arms Dolos Kit can be found on the following link:
https://pantheonarms.com/pages/support
This will fit on the regular Ruger AR-556 if you swap the front sight gas block for a low profile gas block. It will also fit on the Ruger AR-556 MPR version.