I think you have a far bigger issue than just worrying about what license you require.
In order to carry out any form of passenger-carrying flight, your company will require an Air Operators Certificate (AOC). The AOC is a document you will need to write (I've never actually seen one properly, but I gather it's usually several hundred pages long). It will describe exactly what your company will do, what routes it will fly, whether it will operate VFR or IFR, what types it will operate - and how it will ensure its pilots are appropriately qualified.
Once you've got that sorted out, you can then go on to think about your original question of pilot qualifications. The question is whether you will be happy to operate 100% VFR, or whether IFR flight will be required. If you can operate VFR, and convince the CAA of the country you are based in that you can operate VFR, then a CPL/Multi should suffice. If there will be any IFR flight, then your pilot(s) will need a CPL/Multi/IR, and 700 hours total time (the minimum for single-pilot IFR operations).
Also wondered what medical I would require, and should I go FAA or JAA?
If you go FAA, you will need an FAA medical. If you go JAA, you will need a JAA medical. If you go FAA, you may find legal problems operating American-registered aircraft within the EU - there are plenty of people who do this for one reason or another, and I'm not sure about all the legal loopholes. Since you're talking about operating in Europe, I would suggest JAA will make your life much easier.
My main point, though, is don't under-estimate what's involved. It's not simply a case of getting the license, buying and aircraft and then ferrying people around - there's far more to it than that.
FFF
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