So do Resin beads wear out?
as far as I know Rainsoft uses a proprietary resin that should never need replaced.
How would I know when to replace the Resin?
every once in a while the resin could break down and turn to mush, the water presure in the house would drop to nothing and bypassing the system would tell you if it was the resin or some other problem.
Where can I get a copy of the recommended Rainsoft maintenance schedule?
as far as I know there is no "normal" maintenance schedule for the whole house systems, although some customers like the idea of an annual check up. My feelings are "if it ain't broke , don't fix it".