Damn shame, flat on the M25 can't be much fun.
I'm fairly sure that the wheel shouldn't fit in the boot. Check your spare, I think it is a 17" space saver, the standard wheels are 18" so won't fit in there, the spare is even a tight fit in mine.
Depends if you want expensive tyres or reasonably priced decent tyres. Lots of people on here swear by the Falken 452s, I just bought a pair to replace my front OEMs and I am very happy with the Falkens. They are good quality at a much better price (Camskill was the cheapest place I found and very quick delivery).
Standard set up is:
Front - 225 / 45 / R18
Rear - 245 / 45 / R18