I would leave the O2 sensors till the light comes on. Some cars are running past 100k miles and still using original O2 sensors. The car won't break down with bad 02 sensors, light comes on, poor gas mileage, rough idling...all symptoms allow enough time for service.
As for water pump, radiator etc...I wouldn't just go changing them just for peace of mind. They could have been replaced already. Water pump, you can hear the bearing when it's about to go, sounds like a "running train" in your idling. But, if you're not observant to the early signs, water pump could just break down and leave you stranded halfway somewhere...
Radiator...usually it's around the plastic neck area where the hose attaches. You can visually inspect for very fine hairline cracks, or run a pressure test.
A good and honest mechanic should be able to tell you what needs to be replaced or done. I wouldn't go to a dealership as they tend to recommend everything done! Just find a good independent BMW mechanic and perform a full Inspection 2.
2012 Porsche 911 GTS
2008 ford F150 Foose Edition
2010 VW Touareg
Gone...2002 Porsche 911 C4S
Gone...2000 BMW 540i
Gone...1995 BMW 540i