ERJ
I stand to be corrected, if the rules have changed and I am not aware of that, but my understanding is as follows;
To convert a non-JAR ATPL, you must have a minimum of 1500 hours on a type heavier than 30k+ Kilos (can't remember the exact figure), a JAR Class 1 medical, a pass in Air Law and Human Performance (2 quick exams) and satisfactory pass in a skill test which is observed by a CAA Inspector. You do not need to sit the full ATPL theory courses.
I apologise if I'm wrong, but don't think I am.
Denise, if the above is correct, then I agree, get the FAA ATPL first.
Cb