PPL
Hour building (TT min.150 hours - 100 hours PIC)
ATPL's - theory (6 - 12 months)
CPL (1 month)
ME (1 week)
IR (2 - 4 months)
and FI in the end if you have any money left, at least you got all your important ratings. (MCC not included)
When you finish 14 ATPL exams, you must complete the CPL/IR within 3 years, the FI you can do whenever you want. Read some of the threads on PPRUNE, Lasors CAA.
I am not saying your suggestion is not possible, but by the time you have done all your ATPL's, and passed them fine, you will not want to get into a predicament of running out of time to complete your IR.
FI courses are quoted around £6500 + another approx. £1000 for extras, thats £7500, while your IR will cost you around £12000 - £14000 - so unless you have to much money, you want to make sure you have the money for your IR to be completed.
Modular CPL/IR/ME should cost you around £24000 + PPL/hour building and ATPL theory course.(Probably another £12000 for the PPL and hour building)
If you do class room ATPL you can complete it within 6 months, if you do distance learning I think maybe 12 - 15 months, from what I have heard of others. I did full time class room, as distance learning just did not work for me.