I don't think he was there very long. They seem to think he flew about 8 hours before crashing -- no way he could've stayed down that low and kept going that long, not even close. Too much fuel consumption.
2] Did he drop to 12,000ft so that at some point west of Indonesia he could get the door open and bail out to be picked up by the person he got an illegal cell phone call from just before the flight?
That would be a crazy experiment. I'm not saying it wouldn't work but I've never heard of anyone attempting it. The slipstream from most of the doors is not located in places that make it safe to jump. He could have depressurized. slowed (with the flaps/slats out) and opened up any of the doors, but it'd be very risky to jump from there. I think there's an avionics compartment under the cockpit, that's accessible from the cockpit. I'm not sure if someone could fit through it wearing a parachute. That would be your best bet if you could get through it wearing a parachute. Any other door, you might end up in an engine (the crew doors up front) or hitting the horizontal stabilizer (aft cabin doors, over the wing).
Cargo jets and turboprops used in the military for jumpers have air deflector doors for static line jumps (side doors) and the aft ramp is well clear of the tail (the jets are T-tail, and a C-130 has a high horizontal stabilizer too). They of course are designed with jumpers in mind. They jump out at 150 knots or less, even with air deflector doors in use. That's about the airspeed limit for the ramp & door too, since buffeting becomes a factor.
When DB Cooper did it many years ago, it was a 727 and he jumped from the aft door under the tail -- much safer than from a side door on an airliner.
Just thought of this -- if he jumped out west of Indonesia then the airplane would have had to climb back up to above 30,000 feet to make it as far as it did (or at least as far as they say the airplane did). He would have had to configure the airplane with slats & flaps to go slowly enough to jump out -- but nobody would be there to retract them (though the FMS could be programmed to climb without anyone at the controls). So I'd have to rule out him jumping out alone without help from inside the airplane.
I saw where the two possible routes that Inmarsat drew up assumed two different speeds south — one at 417mph and the other at 518mph. That’s quite a difference.