Any advice on running old school Fiat 500

[StoatWithToast]

Hi,

Looking at getting a small fleet of old-school 500s. Probably nothing top-notch, but a few clean examples that are good runners and not too rusty.
We're used to doing a lot of spanner work on older cars, but usually leave the engine and gearbox internals to people we trust with them.

Anything serious / annoying to look out for on them?
Anything made out of unobtainium?
Anything the costs loads more than its worth to fix?

Cheers,

Dave