Yeah, I'd probably use bedroom 3 as an office.
Granny: The left-hand wall (north-facing) is an outside wall that is then covered with glass panels, which is why it looks strange in the diagram.
I don't mind the small-ish master bedroom as I will only use it for sleeping, and I think the smaller ones are still big enough for a single bed and desk/chair, if I have kids eventually.
Thanks for all your feedback, everyone! Keep it coming!
P.S. When we exhaust this particular layout, maybe some more people can post some of theirs and it can be an ongoing thing. Analyzing layouts is fun.