So looking at these cars (2012 age with less than 40,000 on the clock). Is there anything to look out for, from what i've read its mainly throttle actuators and big end bearings, although i'm not sure if either of them give advanced warning and whether the bearings are that common at failing (i'd guess more likely on a high milage car).
You can get an idea of the bearings condition by doing regular oil analysis, usually with every oil change. The bearing issue is blown quite out of proportions and honestly I think a very small percentage of them get issues. BMW did re-design them after 2011 but only changed the material, clearance stayed the same. I have mates that own 2009 and 2010 models with well over 70k on the clock on the original bearings with no issues, and some online report over 100k on them.
Things to check for. Run-in service. Should be carried out between 600-1200 miles, try to coax the seller to tell if he's used launch control a lot or at all. It tends to put a lot of strain on the DCT and wears out the clutches like mad.
If car has over 20k miles, ask about DCT & diff oil change. Even though BMW claims it's lifetime, the gearbox and diff manufacturers recommend done with every 3rd engine oil change. So it's good to know if the seller has done it.
Running costs and maintenance is not that bad compared to your everyday german car. Shop around for your usual stuff in advance and get it on offer.
Discs - £1200 including fitment
Pads - £400-500 including fitment
Oil change including oil filter, air filter & microfilter - £320
Tyres - £800-1000 including fitment
Fuel consumption - 18.9 MPG City and 25-28MPG Motorway. Full tank range City 250 miles, Motorway 350 miles