If you take the ATPL exams for the issue of a PPL don't forget that that you have a time limit to get you CPL/IR and ATPL issued or the exams will expire. You will not want to have to re take them.
Sorry don't know the limits as it's 20 years since I did my written's and things might have changed.
The PPL exams are not hard and not really a burden to pass but perhaps a financial iritation if you are you going to complete!et an ATPL in the future. I would suggest that the ATPL books might rather muddy the water if you are only going to sit the PPL exams initially.