Hi that rust at edge if perfectly normal and doesn’t effect pads , only the middle of disc should be shiny after driving. It can be tapped off with light hammer touches. But if too much can mean discs need changed.
Easy enough job , but small retaining screws , always rusted , I just chisel them off . Calliper back plate has two tight bolts so a long breaker bar needed and a piston retraction tool to push piston back in fully to allow for new pads.