krazy, just wait until you've been a medic for a while. I know 'full-time' medics that haven't used even half the stuff they learned - and I know volunteer *very* part-time medics that are just crap-magnets that get every stinkin' thing in the book. And even after being a medic for a while, there are calls that you never are really comfortable running (kid calls for many medics). And skills you are never really comfortable doing (IOs, crics are common here - I know veteran medics that have never done these skills on a patient).
As for being an I - depends on your system. There are systems in Colorado that don't recognize an I, so you are treated as a B. Also depending on the state, you may have to call in for everything but D50, O2, and narcan.
Basically, OP, it depends on where you are, what access you have to working, and what kind of system you're working in. We can give you all kinds of advice, but unfortunately most of it is pertinent to our particular areas/agencies/protocols. P seems to be out for you based on time, money, and return of investment (using skills and actually learning to be a medic). I would NOT recommend doing the I until you worked as a B for a while (and depending on your system you may not be able to go through I until you've been a B for a while).