We have a 2012 Mini. Owners manual specifies oil that is LL-01 or LL-01 FE certified. The most prolific oil meeting that is Castrol EDGE 0W-40, which is a fantastic oil and a great value.
As for the car, be prepared for repairs and stay on top of maintenance. The engines are notoriously repair-prone. Being a direct injected turbo engine with a small oil sump, I would do no more than a 5k mile OCI. Recommend a good aftermarket air/oil separator to keep carbon buildup in the intake ports and valves at bay. Spark plugs also need to be done every 40k at least. It’s amazing how nasty they get and how much difference it makes changing them.