It all depends on the type and size of airplane.
You can board it and you can also fly it.
Airport
Yes.
Yes.
3 sandwiches
Depends on the make.
You always board an airplane on the left because the right side, whether having one engine or turbofan or two, is running to supply the aircraft with power.
Everyone on board would blow up
Probably, but they might want to inspect it first.
A spacecraft need a rocket engine (which is powered by on-board oxygen and fuel) to propel itself, an airplane only needs a jet engine (which only needs on-board fuel as it uses oxygen form the air).
yes, as long as you are not driving it on a legal street.
If you are travelling internationally, you won't be allowed to board the airplane. Internal flight, it doesn't matter.