Ideally I would like to see something that looks identical, or at least very similar to the prod site+flow (mind, at localhost:3001, etc.), except instead of entering a username and password on the login page, you just enter the username. Assuming the user exists, it proceeds mirroring the prod site+flow again.
The biggest confusion that I could see here would be the generation of client IDs/Secrets, (having seen several people ask how to generate one via the api), and the redirect URLs. Assuming all endpoints used a /mock/ prefix then I see no reason that creation them via the mock api would add too much confusion.