Thanks for the reply. I hadn't ever heard about Tonk strips and it potentially solves the problem that I have for precise book sizes needing to be accommodated. I do have access to a router, so even though I've never used one before I could potentially sink the strips into the side pillars of the bookcase.
What would you advise me to do with the side pillars? Should I just get extremely thick MDF or is there a more elegant or effective solution? Using two strips together, perhaps? Strength is key for this project though and I do intend to screw it to the wall. I had intended to get a framework up using some softwood strips of roughly the size you mentioned. If I were to use the Tonk strips however, would I want to fix the supports you mentioned to the back wall of the shelf as well?
I've never had a good deal of wood cut to size before. If I gave them cutting plans would they be able to get the wood exactly the sizes that I need them?
Looking ahead to finishing the wood, would I be better to treat and paint the strips before-hand, or should I just paint them once they are in place?
I'm sure I have more questions, but I can't pull them out of my inexperienced head yet, but thank you for getting me on the right track so far.