Assuming this is a 94Ah car, then unless you’re spanner handy do not buy privately. I’d only buy from a garage with BMW 1 year warranty. Most independents don’t understand the nuances of these cars. You can get a health report on the HV battery using the hidden button on the screen. No real reports of battery degradation on these cars, even older ones. The 12v battery does need swapped if you get lots of electrical faults, probably around the 5 year mark. Only £100 or so and needs to be coded to car.
Windscreen, check for stone chips at outer edge. They are quite susceptible to cracking If left untreated.
These cars can be scanned with BMW ISTA software for faults. You want history and lots of it. Although the actual engine has probably been used for a fraction of the mileage of the car, the engine benefits from being used. The engine oil, pollen filter are annual, spark plugs possibly every 40-60k miles. I‘ve changed wheel bearings, top mounts, suspension gaiters, PDC and PDA parking sensors, but that’s basically wear and tear and on higher mileage car.
Get the colour and interior you want, with rear camera and upgraded Harmon sound system as retrofitting is expensive. On cars with diamond cut alloys you’d be advised to get a set of winter rims to keep corrosion at bay. Bodywork should be clean. On 2019 cars they will be LED headlights.
Car uses regenerative braking, so as a result brakes do get corrosion unless used, so check discs. Any lip on them I’d be looking to get them changed.