I can’t speak specifically to Vyvanse, but I think I can help with number 3.
I was also diagnosed as an adult and I am on a 54MG Concerta daily dosage which is supposed to last 12 hours or something. I found that in reality, it is only good for maybe 8. As a real estate broker sometimes I am working until 10 or 11 PM. My doctor prescribed me some regular Ritalin to cover me when the Concerta wears off. Perhaps an as needed lower Adderall pill would help a lot.
The ADHD meds definitely made my already night owl habits a bit worse in the first year, but that has improved over time to the point that I can even sleep on the meds when I am really tired.
Best of luck!