Drones 5 is required to field 5 drones (duh).
Additional drone skills mean additional speed/dps/tank for the drones. They're your drones, so your skills determine their outputs.
Is this because some of the medium drone skills or race drone skills have light drone skills as a pre-requisite? I can't comment specifically on Maelstrom fits, but I know on a VG-fleet Vindi I carry light drones (Navy Acolytes)...