Can I use it fully offline?
How do I back it up to USB drive?
What does the day-to-day operation of Pass compared to Keepass look like?
I am trying to learn it as I want to use it, as I think that keepass is bloated for my use case, and I would appreciate any help here.
I second that. The official documentation is always the place to start.
Then, if you need more info or other explanation I usually recommend looking at the arch wiki. Whether or not you’re using arch, instructions there are valid and one of the best you can find.
Finally, this tuto may help you as well