Im not really familiar with diesels but have an e39 close to 3 years now

Coolant system is the weakest link on them budget 500e for it if there is no history of it been changed

Arbs are around 40e for front same for rear but at 180k the suspension will need a change arms,tierods,bushings,probably shocks and springs too thats another 1k easy ,it might be fine to drive as is for the moment and you wont need to do this straight away

The gearbox been done is a big plus
Just go out and view it start it from cold and let it idle while you look around it take it for a test drive on the motorway and backroads if possible