I think 6-8 dailies, one or two per-encounters ("signature" spells), and 2-4 at-wills. You can cut out the signature spells with no real harm done, as long as the at-will spells are still worth a turn at high levels. Starting at fewer is fine, but I think you should reach this level fairly quickly (by 5th level) and stick around there up through level 20.
I've posted it elsewhere, but here's a way wizards could more quickly reach a decent number of spells/day without zooming past it too an overwhelming plethora:
Code:
Lvl 1 2 3 4 5
1 2 - - - -
2 4 - - - -
3 4 2 - - -
4 4 4 - - -
5 2 4 2 - -
6 - 4 4 - -
7 - 2 4 2 -
8 - - 4 4 -
9 - - 2 4 2
10 - - - 4 4
Since spells can be prepped at higher level (and some of them even get a benefit from doing so), this allows wizards to stick at 8 spells per day indefinitely while continuing to increase in power.