The thrust vector should point through the center of gravity for stable flight. If the thrust vector does not point through the CG, you will get a rotation on the aircraft with the CG being the center of rotation. This is how aircraft get such small turn radii with vectoring engine nozzles. Many rockets use vectoring nozzles to steer based on the same principle.
EDIT: Added more explanation about why this matters.
That entirely depends on where you put the motor. I feel like this really needs a video or a bunch of diagrams to fully explain. I might be able to put something together later or others can jump in if they have the time and means