Answers based on personal experience & what I have read over the years:
How long after quitting finasteride should I expect hormone levels to return to normal?
I am not a doctor but most people say one month. When I gave up it took 4 weeks to feel 100%.
How long after quitting finasteride should I expect the (potential) psychological symptoms to subside?
Same answer as above I would think, assuming there is no secondary issues (e.g other factors like work related stress).
How long after quitting finasteride should I expect hair loss?
After prolonged use I think most people would say '4 to 6 months'.
Assuming that I do notice a disappearance in symptoms, and decide to get back on finasteride at a lower dosage:
What is the lowest dosage that has been proven successful for long-term hairloss?
I saw an amazing result posted by Dr Bill Parsley.
http://www.hairrestorationnetwork.com/eve/168490-dr-parsley-results-1-4-tab-propecia-0-25mg-daily.html