Congratulations on getting your RN!

The "P" does stand for Paramedic. State laws vary widely, but you may be eligible to challenge (test without taking the course) either the EMT-Basic or Paramedic exam for certification. In some states, an RN with EMT (by course) certification can challenge Paramedic. An existing EMT certification (and, sometimes, field experience) is almost always required for admission to a paramedic program or for paramedic certification.

The entire EMT + Paramedic curriculum, with pre- and co-requisites can run about 2 years, but would be maybe about a year with your RN.

EMT-Basic programs are usually just a single semester, single class course, maybe 5-8 hours per week. Paramedic programs for EMT's typically run about a full calender year around here, and are quite a bit more intensive and time-consuming than EMT classes.

There are also "cram" courses that teach EMT or Paramedic in much less time, usually by for-profit providers, but the quality of their product is often not well regarded. However, since you already have an RN, you have enough clinical credibility to overcome doubts, and one of these may fit your needs.

I'm sure you're aware that pre-hospital emergency medicine has, in part, it's own unique skill and knowledge set that must be mastered and is usually not taught, or at least not taught well, anywhere other than in EMT or Paramedic school, not even in PTLS, etc. Things are sometimes done differently in the field. A code in the hospital, with a patient in bed, a full code team of MD's, RN's, and RT's, in a roomy, well-lit hospital is not like running a code all by yourself on the floor of a filthy, cramped mobile home bathroom (if you're with an EMT partner, you do all IV's, all advanced airways, push meds and run the monitor by yourself, plus you gotta pick up and move it all to the ambo at some point) In addition, you deal with some things that aren't strictly medical, like hazmat and extrication. Therefore, I'd respectfully suggest at least a full EMT course, and then challenge the Paramedic if you want.

Your paramedic recertification usually can be kept current just by completing CEU's, without having to work. Your state may be different.

You can work or volunteer for your local rescue squad, FD, or Ambulance service for experience, but you may be restricted to BLS only, at least at first, since practicing ALS, even if you're a certified Paramedic, will usually require knowledge of, and testing on, local protocols, approval of a medical director, and direct verification of your practical competence by observation and experience with a field training officer.

Most FD's want you to have firefighter certification, but some run EMS separately from fire suppression. In addition, you may need various "merit badges", some of which you likely have, such as ACLS, PALS, PHTLS, EVOC, HAZMAT, before you can work on an ambo or rescue.

Edit:I got distracted and didn't post this until some time after I wrote it, which was before all the other good replies were posted, and I didn't see them before I clicked "post." Sorry for the redundancy