Ok so I have some results. They aren't really good. (Note: these tests were in regard to skill gain, if you just want books you will get them eventually with a group of random freshman scholars)
First, scholars can do the following activities to gain skill;
1. Ponder; this is an individual activity.
2. Discuss; this is a group activity with at least one other dwarf.
3. Learn/Teach; this happens between master and apprentice. Dwarves will form the master/apprentice association when the master dwarf has a high level (lowest I saw was expert) in an academic skill and the apprentice is low.
Second, leveling any academic skill is painfully slow. Dwarves gain between 5-30xp per activity, this is dependent on various skills but each activity happens at random, and competes with other leisure activities like worshiping or listening to music. As such, getting a dwarf beyond dabbling is nearly impossible.
Third, around 50% of the time dwarves will engage in an activity that is related to a skill they know. For instance, a surgeon will talk about medical stuff half the time. However, ANY academic topic can be chosen for an activity. This means that over years of time every scholar that participates in library activities will gain dabbling in every possible academic skill.
Fourth, dwarves only gain student and reading skill from reading books. Dwarves do not gain topic related skills from reading.
I tried various things to boost skill gain. I tried different numbers of scholars. First I tried several small libraries with 1 expert and 4 freshman scholars. This didn't work so well because the freshman sat around thinking of random topics and the expert was busy writing books. Then I tried a massive library with 50 scholars and the same thing happened only on a large scale. So, basically the number of scholars you have doesn't matter aside from the amount of books you can crank out per year.
The library does a good job keeping medical skills from rusting but don't expect to create a dwarven madam curie.
My advice if you are looking to get a library going is to embark with the academic skills you want otherwise it will take decades of in game years to get anything other than dabbling. I personally always embark with a doctor. Now ill just slap some writer points on there as well and call it good.
Also note, scribes don't matter. They just copy books. They can be anyone. You could just draft 5 or so random dwarves and they will occasionally copy a book for you.