The motor is probably ok. The problem is either with one of the impellers or a foreign object inside the pump. You won't really know until you take the top of the pump off and see what's going on inside.
If the pump/motor seal did not break and the motor is ok, you can rebuild the pump using a
pump impeller kit.
Breakdown diagrams for
Model MDB4100AWW
As far as your fourth question, I don't think this type of a problem has anything to do with any specific dishwasher model. Same thing could happen to just about any dishwasher out there. Maytag dishwashers are not that bad at all (for the price).