As always, get a PPI done by a trusted indie BMW mechanic. Get recommendations from a local chapter of the BMWCCA if you don't know someone to ask.
Also, get a Carfax report if you can.
That straight six is a wonderful engine.
The cooling system is something you want to have checked out because if ignored, it can bite you. Many recommend replacing all the hoses when you begin ownership.
Especially all the small hoses on the right side of this diagram:
https://forums.pelicanparts.com/off-topic-discussions/1122521-best-place-measure-engine-water-temperature.html#post11739177
They sit near the engine and are very likely cooked and brittle if they've never been replaced.