Google Lasors CAA, there you will find all details exact as required.
PPL theory (8 exams) + PPL + Night Rating + ATPL theory (14 exams) .
150 hours total time (minimum 100 PIC, 20 hours cross country)
Rarely does anybody make it in minimum time, to be honest I would probably add another 20 - 25 hours to be safe.
Furthermore from the date you finish your last ATPL exam, you must complete your CPL/ME and MEIR within 3 years, if you only do your CPL and exceed the time limit you have to take all the exams again. (and that's no fun)
Integrated will cost you twice the price of modular, and will not be step by step. And will not give much if any advantage in today's job market.
Going to USA, will not be a huge saving, you still need to do the 14 ATPL exams when you return, and the conversion costs is not cheap either. Might be good experience, but if you are on a budget, you also have to consider expenses of moving to US, and living there, you probably will come out similar price as modular in the UK, if not maybe a little more expensive.
PPL will probably take around 3 - 5 months in the UK (weather can be problem) ATPL theory minimum 6 months for the 14 exams (Maximum 18 months from first exam), hour building - again, how long is a piece of string? CPL training around 4 - 6 weeks (weather dependant) Night rating 5 hours.
ME 1 week, and IR around 2 - 3 months (I can not emphasise enough, do not run out of time from your last ATPL exam completed.
Modular the PPL + CPL probably will cost you around £22000 - £25000. (with IR & ME around £40.000 - it is money to be saved depending on if your son can do it in minimum hours)
Remember the adverts always state MINIMUM HOURS, requirement, if you go over you pay, specially take note of this for the FAA and conversion.
Minimum hours conversion is 15 hours, but I have heard of experienced pilots spending 30 hours (each hour approx. £350 in twin/IR conversion)
The £40.000 is a rough price, which includes contingency for more hours then the minimum. (prices does never include exam fees - CPL skill test and issue fee is nearly £1000)