1. nothing to stop you starting study for exams
2. as it stands at the minute, you would need to do an IR within 36 months of passing last ATPL exam or else, beyond that time, sit the IR theory exams (7 of them) similar to cpl level but shorter I think.
3. ATPL slightly more involved than CPL but it depends what you want to do with your licence. Do you want to go offshore? Stay onshore? If you plan on holding an IR, do the ATPL's.
If you want to work single pilot onshore, do a CPL. You can't hold an ATPL unless you have set number of hours/number of night hours/multicrew/IR/multiengine? I cant remember the exact requirements but look in LASORS for info.
Good luck with the PPL
