Don't use random encounters and don't use the critical hit, they are for later. Supply the wizard but let your opponent pick out the spells. Make sure he/she knows that high casting values are not very smart to start with, because he/she might be as tactically challenged as me and pick all the wrong ones.
Other than that, part of the fun for anyone, experienced gamer or not, is tailoring the spells to what you like, so I would definitely allow your opponent to do that him/herself. I also think that by doing so, the player will get a fairly good indication of what the game is about.
As for what type of wizards... if you have plenty of stuff lying around, why not give that choice to your opponent as well? Simply give a real quick and dirty description of what they all are, and let him/her base the decision on that description.