PPL Pointer 1: You do NOT need to convert your FAA PPL to a JAA PPL if you plan to go on to your JAA CPL/IR. As an ICAO PPL it is valid but will be restricted to day VFR within the FIR. Save some cash where you can!!
PPL Pointer 2: You could do a JAA course in the USA and therefore could ignore point 1 anyway.
ATPL Distance Learning: It is hard! Motivation is the biggest problem. Yes everyone is motivated to be a pilot but you need to also pick up the books regularly!! I am just about to sit the 2nd set of 7 exams next month. It has taken me 7months full time to get to this point (I stopped work for the course). I have worked 10years in aircraft Flight Test and that helped a lot. I can see it being a steeper learning curve for others. (Not boasting; just saying)
General: This is a costly and time consuming venture. If you are going to go at it full time and finish ASAP then fine. If you intend to pace it over a few years so that you hours build, work and study in parallel expect it to be tough!! BUT good luck!
See you in the crew room one day!