Mini Coopers have multiple airbags (side curtain, driver/passenger, seat airbags etc...) The doors are steel inforced with 3 steel beams through each door... VERY SAFE VEHICLE!!!
As for maintenance... It seems to be a good car so far. I have 247 HP in mine and it has lasted me 30k so far... I see them with 78k or so on them on autotrader, so I would think they are good for 150k.