My steering wheel is starting to shake once I hit a certain speed (50 mph).

Sounds like a tie rod in your steering linkage or possibly a ball joint. Either way you need to get that checked,sooner than later.

I am NOT a mechanic, but my 2004 saturn ion makes noise over potholes and told it is the bushings. As to the shaking over 50mph, do you have tires aligned and regular rotation