Rich,
Correct me if iv understood you wrong but it's not as simple as you are implying below.
A. You cannot upgrade your licence from a PPL just by completing the ATPL exams and flying hours. In order to upgrade you would need to have hour built from PPL, gone through a CPL flight course, passed the flight test and already have your ground exams in the bag. No point in starting the CPL work unless you have a Class 1.
B. Tricky one as on your licence you will have CPL until you have got all your flight experience and passed your ATPL Assessment and applied for the licence. If you don't have the Class 1 you cannot exercise the privileges of that licence. I'm sure someone in the know will let us know if you can fly on a CPL on PPL privileges with a Class 2.
It depends entirely on what you want to do. If you aspire to gain an IR or actually achieve your ATPL you must do ATPL ground but you must get your IR within a set time of passin the exams.
LZ