I'm so pleased you liked it, and what a thoughtful and detailed review!
The Hamish part was mostly a self-indulgence, a cheater's way of borrowing a familiar character and locale, that I just then had to describe, but if you ever get the chance to see them, the series can be rented (3 seasons), and they're wonderful.
Glad to hear their occupations 'fit'. And Snape finding something he loves to do that isn't magical, well, like you said, audiobooks seemed a natural.
And you're right, I think, that Snape would obsess, particularly over something he believes he's lost due to his own weakness and foibles. It felt really good to give it back to him, and to have him teach Harry that lesson. On top of that, Snape would want the best for Harry in this story, but had a hard time believing he deserved what he wanted. He expected noting, and Harry, being Harry, gave him everything.
I really appreciate that you made the time to read; it means a great deal to me. Thanks so much again. ♥