Volley = How much damage you do with 1 round of all you weapons at the same time.
Also referred to as alpha.
Rails vs. blasters... Dunno. If you fit blasters you can work on the big stuff while the drones do the rest, you're right there to salvage/loot. Rails are quicker to pick out and shoot targets which requires less travel (bring your salvager back to loot.)
I'm looking forward to trying out a Domi in various configurations.