if you are looking to do 911 response then you will probably need a year + experience. The only case where you would have to take extra courses is if the agency that hires you requires you to have CEVO and/or EVOC to be a driver (Certified Emergency Vehicle Operator/ Emergency Vehicle Operator Course).
As new EMT-B, the jobs that will probably be open to you are routine facility to facility transports. This often consists of moving an invalid from a nursing home to a dialysis center and back again. If you want to do this then thats cool, however in my opinion, it is a waste of time and skill. You will not get much emergency experience as a transport EMT.
In the hospitals...some hospitals hire ER techs who basically take blood pressure and put patients on O2. Again, this is not really a worthy use of your certification as an EMT. But then again, if you need money...whatever pays the bills. Hospitals may require you to take facility specific protocol courses.
I dont see you having to take any additional courses aside from CEVO or EVOC. But then again, depending on how strict the agency is, you may need to take some additional certs like hazmat awareness, WMD awareness, fire scene awareness, etc.
Now another problem you may run into as a young EMT (which is what happened to me when I started) was many agencies may not be able to hire you until you are 20, 21 or older. Their insurance that covers you may not allow 18 year old workers. Also many don't want students. They need more coverage then a student can give.
I hope that answers your question. Good for you for becoming an EMT. I hope you take advantage of it, especially at your vollie corps. This country is very short on volunteer EMT's. Enjoy!
My advice to you is this: Find a busy volunteer corps, put some time in and get experience, make connections and you'll get hired soon enough. You don't know enough to work paid yet. As a paid EMT your agency will NOT back you up if there is a legitimate lawsuit filed against you. They will fire your ass and separate themselves ASAP. Get volunteer 911 experience for about a year--try for 200 calls before you go paid. If thats not reasonable in your area then try to get 100.