One thing you need to know is what was the pre-first-year VED invoice price of the car because if it was £40k + you're in for £450pa VED for 4 years. (Under £40k: £140pa.) If it's been outside the brake discs will have rusted so, even though the rust may have cleaned off you need to make sure the discs are not grooved. Wise to have the brake fluid changed because sitting around fills it up with condensation. It's wise to change the engine oil and filter plus it will probably need a new battery (expensive with BMW's stop/start system).