Toby,
My discs and pads lasted about 30k at the front. I replaced them with the JCW drilled and grooved discs with Mintex 1144 pads. Wouldn't really recommend the Mintex actually - would suggest to stick with the OEM pads which are Pagid I believe. The discs look nice but doubt they do much -
clicky.
Next time round I'm going to stick to the same discs but have them coated by Nitrac, then a set of Carbotech pads.
Sensors ain't a problem, and they can be reset via the rev counter with no need to plug into diagnostics whatever BMW tell you.