I think they should be on-topic.
Libraries are an important part of the literature community as they provide access to the public of the works we love. I'm sure many experts of literature have spent a good deal of time in libraries. I also do not see a current SE Site where they would be on-topic, so here is a good a place to attract new users with new questions that they may not been able to ask elsewhere. (As I typed that out, I realized there may be some overlap with Academia depending on what their scope is.)
To address your specific example questions:
- On-topic, but would might be downvoted as a lack of research (Google bring up a one-box when you search).
- On-topic, but has a slight possibility to be too broad. Although, I'm sure there are some accepted ways that could make a good answer.
- On-topic, and I see no issues with it.