I’m not really an expert in the topics you’re talking about but since noone answered so far, I will say what I think.
…is it possible to run pre- and post- repository access scripts within rest-server, with the argument of the path that rest-server wants to use?
rest-server just accesses a standard folder that contains a normal restic repository. You can run restic on the machine that runs rest-server and do any maintenance work that way. For instance you can check and prune the repos directly on the server.
My second question
It doesn’t sound like restic is a good fit for that to me. The splitting into tiers is a complicated way to deal with scarse drive space. A complicated system with so many components introduces many points of failure that all have to work in order for your backup to work. I think this only makes sense if you really have gigantic amounts of data and even then there’s probably a reason why there are different approaches used these days.
Check out the restic documentation as it contains a bunch of details on how restic works under the hood. It’s well written and fairly easy to understand.