So a frozen ATPL is when you have everything you need for ATPL apart from the hours? And i'm guessing most people get their hours whilst working? Or do you need 'buy' your own hours up to 1500?
That's pretty much correct, a fATPL if that's what we're going call it, is when you actually have a CPL, have passed the ATPL theory exams, probably with a MCC course and IR. But you don't have some or all of the various hours requirements.
Yes, most people will get the hours between CPL and ATPL by working, you could "buy" them, but as has been said by myself and others, it'll be expensive.