1) I understand the gravity/momentum transference, but didn't the chemist specifically state that the kick still worked because inner ear function was not impaired by the sedative? By that logic, when the van flipped over and hit a pole, shouldn't everyone have been bumped back up to that level?
They didn't feel like they were falling because they were strapped in to their seatbelts tight as heck and always had that comfortable seat as a base. At any rate it wasn't a strong enough kick, they were sedated on the first dream AND the second dream, which they also would have had to be woken from first.
2) If gravity was required for the kick in the second level (since the van falling in the first level caused a loss of gravity), why didn't everyone wake up as soon as their bodies hit the floor when the elevator was blasted by the explosives? Why didn't they wake up until the elevator crashed?
It was zero gravity, it wouldn't have started out moving that quickly until the elevator gained momentum from the blast. o_o The hit at the top, that also probably would have "killed" them, was a strong enough hit to wake them up or kill them or whatever.
3) The totems are presumably based on physics since Arthur explains that his loaded die has a specific weight that only he knows, so as to confirm his anchor to reality. So how exactly does Mol/Cobb's totem actually involve any physics if the only indication that he is in a dream is that it spins endlessly? And by telling Ariadne that it does this, hasn't he invalidated the security of that totem? Couldn't she purposely create a totem in her dream that would fall instead of spinning endlessly?
Not sure what you mean here. Nobody touched Cobb's totem, so the weight, shape, and texture of it is only known to him. The fact that it spins is not necessarily the most important aspect of the totem. You don't see Cobb there telling Ariadne the exact weight of his totem in grams, or letting her touch it. Nobody touched it except him, the same with all of their totems.
In hindsight, what doesn't make sense to me is why they all didn't just shoot the people in the heads when they were done instead of using a kick, since that basically works the same way, didn't it?