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.