Answers:
As you can imagine it won't be as strong without the layer of skim, it's just quicker and cheaper. it won't crack. it's a common finish on new builds these days.
Sounds like a bodged job, you don't put plasterboard between two layers of bonding, it should have been all filled in with just plaster.
Yes, that's standard practice to dot and dab on bricks.
plasterboard is not designed for carrying heavy loads.
You don't scrim internal angles/corners. you put beads onto external angles/corners. no, you float walls first, then skim.
Plaster will draw moisture off the floor upwards and get damp. you leave an inch gap off the floor and put skirting boards on.