As I've told you before in other threads, the FAA route is cheaper if you're going "all the way", which you are.
The PPL is just a stepping stone so it doesn't matter which you get, you certainly don't need to convert an FAA PPL to EASA - you can go straight to CPL.
If you take the FAA route, you only need PPL and multi IR - you don't need commercial. This is because the FAA commercial is 250 hours, which means 270 hours by the time you convert. That would be daft since the EASA CPL is only 200 hours!
If there's one thing I've learned from aviation - whatever you plan now will end up being completely different. All routes start with a PPL. Get your medical, get a PPL and then stop flying and pass the ATPL exams. That's the hardest bit. IF you make it that far you'll know by then what the rest of the plan is and you won't have borrowed anything. The good news is an fATPL won't cost any more than £40k so you won't need to borrow anything until the final few months.
And you don't need to give up work.