try refining the search by only searching in the areas that will answer your questions.
But to give you some help:
The car is pretty much bullet proof as long as it has been regularly serviced at the intervals you have posted. Obviously if you can get a car froma a forum member your on to a winner as it will have been VERY well looked after. You have already listed all the major faults.
As for a garage in the North East i cant really help as im in the south east, i know RS tuning, a trader on here, is in leeds. Im sure some of the more Northerly members can help you out there.
If you look at the portal home page of the site you will see a list of traders such as Envy Performance (z-store) CS, Z1 (States) rare Rims etc aswell as member traders who can also source new or second hand parts.
As for the bose, mine is shocking so im replacing it straight away. If you search in the audio section you will see a whole range of aftermatrket options.
Hope this helps