I am an EMT (starting Paramedic School soon) and thinking about joining the Marine Corps Reserve after paramedic school and wanted to find out what type of MOS to look into and if I should finish out my BSN first if I want to go Officer.

Greg,
Welcome to the boards. There is a lot of information in a lot of different threads here. I would suggest you go HERE first. Do some reading, then we will be more than happy to answer questions.

For the reserves, a recruiter will be the best source of info. The types of MOSs available is dependant on the type of unit that is near you. For example, there will not be infantry slots available with a supply unit.

BSN? Bachelors in Nursing? If that is correct, you may want to look into the Navy programs for nursing, if that is what you are looking at career wise.