What are the benefits (if any) of disclosing a mental health diagnosis/disability?
I'll answer this part:


  are there benefits to disclosing a serious mental illness



If you are teaching, there are benefits to your students.  Many students have disabilities.  Students do better when they see successful people who are like them.  These role models increase students' belief in their own abilities, which is called self efficacy.  Students with higher belief in their own abilities learn more.  If you disclose your disability, it will help students with disabilities succeed academically.
For hiring and promotion purposes, some institutions consider performance relative to opportunity.  This sort of assessment is common in Australia, for example.  If your disability has reduced the opportunities available to you, then disclosure may make your achievements seem more impressive.


You did not ask about the potential disadvantages.