I like the school option. I don't think a singles is necessary. As the game grows in popularity, there is sure to be a secondary market crop up (I've already ordered and received from one site that seems to be going this direction). Secondary markets are good for games because those dealers often buy a lot of product to fill their stores. I would think that selling singles directly from the developer would kill any chance of a secondary market, which is, IMO, not good for the game, overall.
Having the mage books is not a good idea, IMO, because that forces players into situations where they are getting what the Dev team thinks should be in a Mage's spellbook, and not as open to interpretation as other options.
My two cents...
-nihil
