Controlling the state of bicycle components
For most of your ?s, I would use visual inspection.

If you always check your chain for wear, the chain rings and cassette will last a long time.

Some brake pads, rotors and rims have waer indicator guides built into them.

Fork is greased, not oiled. Fork is inspected for cracking, a weak point is below the crown.

Frame should also be inspected for cracks.