On the rust issue, I’ve just watched a YouTube vid by the wood whisperer about a new (to him) product to stop rust on cast iron tables etc. The initial test looks promising. Might be worth a look.
For induction motors, there should be no problems whether you run on 50 or 60 Hz
The motor speed will be different x 60/50, but that should not be a problem.
After all, that is what VFD's are designed to do !
The induction motors that I run of VFD's are happy to run between 20 - 80 Hz