The rear guard team was Garrus, Tali, Miranda, Legion, and Mordin. That's indeed not a terribly powerful force.
I also played on Hardcore, which I am not sure I did before. Unless there's an achievement for that, in that case I did do that before.
I am also planning to do a Let's Play in which as many people as possible die. I heard that one needs at least one party member to survive or Shepard dies in ME2 and I think I'll take Thane for that, since he's already a dead man walking.
Unfortunately there are killable NPCs in most loyalty missions which I also would like to do. Figuring out the maximum death count will require quite a bit of planning.
You can get a member's loyalty and then kill them off by intentionally choosing something they can't do, (i.e The tech mission)