Thanks for the gas block replies, fellas. I'll probably go with 15" handguard if it means better protection for the block.
For the handguard I've really been eyeing up a Brigand carbon fiber blade with the m-lok slots. Hmm, given the blade feature, I wonder if it's measured 15" from the longest point at the bottom of the blade, or the shallower top part...
As for the buffer situation, I ended up buying an Odin Works adjustable carbine buffer. I was sent a great info graphic from them to help me figure my set-up out!