Hi Ian, welcome to SIDC [Y]
Having only recently purchased an 06 STi from MP I have to say you have covered pretty much everything above. The one thing I did find interesting was that MP only offered me 600 quid less for my trade-in (53 plate WRX, 1 Owner, FSSH, Immacualte) compared to 3 subaru dealerships I spoke to. I had to haggle a bit to get the trade-in up a notch, but this was not difficult []
I am not quite finished dealing with mp as yet though, after 5 and a bit weeks I still don't have my service book [] Should be here soon though. Not having the service book did not stop Nobles doing my 1000 mile service on my car though, and they will stamp it the next time I am in!
Good luck,
Neil.