One thing that should be mentioned is that even big brake shops
and professional mechanics seldom rebuild calipers themselves. Rather they usually send them to a local brake rebuilder who has the parts and equipment to restore the piston bores properly if needed.
While I do replace brake pads and have rotors turned myself if needed,
I take any caliper rebuilding to the local brake rebuild who usually has them done the same day if taken in by noon. And the cost which usually isn't too bad includes "loading" with new pads which you can either use or replace with better ones. The shop I use has been in bidness forever and even has
rebuilt exchange calipers for some Opels ready to go.
In the meantime while waiting for the calipers to be finished, I repack the hubs and have any rotor work done.
IMO, it just isn't worth the time, work and mess to rebuild the calipers and wheel cylinders myself for what the local shop that caters to the mechanics will do it for.
Jmo.