The DDM4 Rail is not listed as a compatible handguard by Adams Arms. I recommend contacting Adams Arms to confirm compatibility of the Adams Arms P Series Micro Block Carbine Length Piston Kit with that handguard.
The handguard requirements are 1.02" minimum from the center of the barrel to the inside top of the handguard and the top rail internal width must be at least .500". The link below will show you a list of compatible handguards. Adams Arms does not state if their BCG is full auto rated and I recommend contacting Adams Arms for that information.
https://adamsarms.net/faq/#1606555356337-ad0a9226-350b
Yes it is .750
The bcg is a full m16 size.
As long as it uses a .750 gas block it will work with it.
As long as it uses a .750 gas block it will work.
No it cannot.
Yes it is.
The adjustable option functions like an adjustable gas block, letting you select the amount of force imparted on the piston. This is typically for suppressed guns.
Yes it will.