The Gear Head Works AR-15 Carbine Spring and Buffer will fit if the SB Tactical Brace uses a standard length buffer tube. However, I do not believe it does so the spring and buffer listed at the link below would be a better option for that set up.
https://www.opticsplanet.com/strike-industries-ar-pdw-9mm-buffer.html
Yes, this should be compatible, but you may want a heavier pistol buffer.
Yes, it would work, but with the 7.5" barrel pistol-length gas system, you would probably want a heavier buffer.
For a 10.5" pistol length gas system you would probably want a heavier buffer, but yes it would work.
Yes, they would be compatible.
Yes, that would be all you need.
This is a standard mil-spec setup with the buffer weighing 3 oz. Gear Head Works sells a Tailhook Mod 1 (non-adjustable) kit that includes this exact buffer and spring, so you should be set putting this in your Mod 2.
Yes, the UBR is compatible with multiple buffer systems, carbine length being one of them.
This is a standard mil-spec setup with the buffer weighing 3 oz.
This is a standard mil-spec setup with the buffer weighing 3 oz. This will work in any carbine length receiver extensions.