Many people do instruct to build hours, as I did, and there is no problems at all doing it as you study for IRs etc
If someone started today on a full-time intergrated ATPL course, they would in about 2 years have an (F)ATPL, MEIR, MCC/ Jet appreciation time, and about 250 hours.
You're planning on doing something similar, via the modular route, and looking to fly 1500 hours in the same time. From my experience in aviation, I feel that the timescale you have set is too limiting. I would realistically expect it to take 3-4 years to achieve your aims.
Trying to pick the information from your posts on various threads, I'm trying to sort out the background to all this. You work/contract for someone wealthy, who has a boat in the Med; they wan't someone to fly a private aircraft there (and other places) for them; you're ex-RAF and ATC and so are there perfect man for the job; you've come up with a plan and a schedule; they're paying for it and expect a result within the specified time?
My feeling is that they don't know what to expect form a 'corporate' pilot but it would be nice to have one; you have underestimated what it takes to become one.
With the amount of money that is mentioned, go and look at Gold Air, LEA etc to get you to the Med. Get a nice new C172 for flying in the UK.