I have both FAA and JAA PPL. If you are going straight in to JAA CPL then all you really need is a ICAO PPL (FAA is okay I believe, I am not at home so I cannot cheak my copy of Lasors).
Hope this helps, also if you do get a FAA PPL then a JAA conversion you must keep the FAA current to keep the JAA one current as well. However I have no real intention of flying on my PPL now I have my CPL.
FF