It will not come with a roll pin. The roll pin is normally included with gas tubes.
Set screw spacing is not listed by the manufacturer. Normally when installing a low profile gas block, set screw spacing is not a real factor that plays into deciding what option is best for you.
This gas block uses two set screws, so you would have to dimple your barrel if it is not pre-dimpled from the factory.
Yes, this will fit under a 1.3" handguard after confirming with Ballistic Advantage. The handguards offered by Ballistic Advantage are all 1.3" internal diameters. This gas block is the same overall height as most others and most handguards have a channel at the top of the internal diameter to accommodate for a bit more height from the gas block.