You could still make him as a Companion if you are interested. There is no "cap" on Companions, just I want at least one Companion from each of us attached to another Magus. If you are still thinking about this.
I haven't spent a lot of time thinking about it but I'd like to find a way to give him some sort of "book magic" (or something) that makes him unique and interesting while transforming his fixation on the Praesis collection of books into a positive incentive of some kind.
Negative incentives I think, especially over time, make for less pleasant and less engaging stories and gameplay. Tension and stakes in stories are excellent but I tend to think of "baked in" negative stakes as a choice that for many people leads to stories they find less fun once they are in them.
Thoughts?