Welcome to the Forum, congratulations on your purchase.
Service history as always is paramount same with any car, also check with BMW for any recalls/updates that have been due and were they carried out.
If your X3 has a staggered wheel set up (wider rear tyres) take care when replacing tyres make sure all 4 are from a good manufacturer differences in rolling circumference can cause transmission wind up and damage to the transfer box. This applies to all X drive cars and BMW recommend * rated tyres. If the wheels are same size on each corner it is more forgiving but you should still check that all tyres are from a recognized manufacturer and the correct size at least then you have a chance the rolling radius is within tolerance. Apart from that they are good cars ENJOY
If the worst happens there is loads of support here