I like the random spell generation idea! It is a simple way to illustrate the unpredictable nature of this rougue mage.
I would however try to find a way to make the wild mage a substitute for the wizard only. I think he can be made to function simultenously with the elf. For instance, and remember, I'm just spitballing here

:
1) The mage chooses a spell school that the elf is NOT allowed to take.
2) The elf chooses a school
3) The mage chooses a school to get 2 random cards from, rather than one.
4) Generate the spells.
This way, the mage still gets 4 random spell cards, and the elf gets a full school. Also, the mage has to make a decision between which school he will be guaranteed to get, and which one he will get two spells from. In other words, he cannot be sure to get two spells from his favourite school
Just a suggestion...