Level shouldn't be an issue. If it makes a difference, whichever level you enjoy the most.At what level?
*snip*
So, assuming 4 encounters of 5 rounds each (on average), the Wizard should probably have about 20 spells (of all levels), *snip*
I like this basic idea, but, I would qualify it as 20 rounds of _Combat_ spells. If this is how much combat a wizard "should" see, then he should be able to be a wizard for that much combat. Exploration and Interaction are much harder to quantify, but it seems likely that you won't need 20 for each or even combined. Maybe 5 exploration, 5 interaction.
So if you only have daily spells, the math says I believe a wizard should have 30 spell slots...even at low levels. Obviously that's just nuts.
If I add at-wills (50% of combat? I think you should have 2-3 to chose from, with level advancement) and signature spells (20-30% of combat? of which you should have 1-2), thats 10 rounds of at-wills 4-6 rounds of signature, leaving 4-6 daily slots....and I'd be fine having that number grow slowly.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.