Everything rubber or plastic is going to be prone to failure. Drive train and suspension bushings, air passage, vacuum hoses, water hoses, etc. If you have the tools to press out bushings and replace them you can stay ahead of it and keep it riding like new for a reasonable cost of operation.
The only parts likely to leave you stranded if they fail are cooling system, so keep a close eye on that.
Mechanical/suspension parts should be readily available from all the major on-line suppliers - Autohaus, Pelican, Bimmerparts, etc. Parts for the convertible top may be a challenge,