More power to ya if you really want to do this, but I would recommend only selling the top 1-2 levels of an enchantment. Maybe top 3 for things like efficiency. All levels of all enchantments is quite a lot of shop chests, and your wares might just get lost in a sea of signs. Also, multiple enchantments; don't go there. Just pure sadness.
Thanks for the advice Erik. The way I was planning to do it (already got a bit of it set up) was to be selling only books with single enchants, and as for layout and getting lost in signs, I'm planning to organise via what type of tool it goes on. This allows for every contingency, for all people. I could show you next time we're both online if you like.