Yes you can't take JAA flight test in the US, they can prepare you, but all test must be done with a UK school in UK airspace.
Saving money, don't think so either, if you calculate everything.
Hour building is probably better in the US, but you might as well do all training with ONE FTO in the UK.
But one thing, you think now is the big difficult question, sorry, after you completed your CPL/ME/IR, that's when the real big questions start coming.
Was fairly easy for me to decide my path until completed MEIR, now I stand with by the major crossroads, which will decide everything!
FIC, TR, ATP CTC, Line training, etc.... Not easy to decide, and as some mention, you will find 1000;s of opinions from pilot to pilot, in the end you need to take chance, decide, hope it is the right choice, and hope you will have the required luck in addition the skills required.
Enjoy the CPL and the ME, they are the fun and easy bits, the IR is the interesting, but the hardest. I personally found few good add ons to flight simulator FSX, that was excellent both for the DA42 that helped to practise and learn the procedures and systems.
I would not bother with this though until ME and CPL is done, because the IR has it's own life!
I would recommend Stapleford, but I am sure anyone who has completed their training anywhere else, and happy there will recommend that school too. Seldom will you find someone training at 2 different schools. Not good for CV, and if you happy you stay! So not many who can compare different schools by experience.