JJ, with your proven skills at managing
light and
exposure I reckon you won't have any problems with simply bouncing
light of a wall or ceiling and having the slip out reflector there to provide a little fill as Matt said.
It sounds like you want to keep it all compact and manageable for one person so on camera ( or a bracket ) will be the easiest all round. It simply becomes a matter of balancing whatever ambient
light there is with your desired level of "freeze" in the subjects with the
shutter and maintaining the
aperture that gives you the depth you want in the shot matching the flash out put. On camera flash doesn't have to create ugly shadows and destroy contrast when used appropriately with a simple set up.