I guess you don't want to drop any wizard levels and lose spell progression. I hope you've got a great CON, because if you get into combat you'll need all you hp!
My suggestions:
Combat Expertise and improved disarm first. As a 2H large weapon quarterstaffs are great for disarms, and improved disarm gives you a bonus and nixes the penalty. Removing your enemies weapons has got to be a great move, right?
For style it is definitely worth spending cross-class skill points (you've got lots, your a wizard!) on tumbling.
I wouldn't bother with weapon focus, I guess you could pick up improved critical (staff) at about 18th level if you really wanted to
(If you were up with sacrificing a level of spellcasting I'd go with Darklones suggestion for Monk though - the quarterstaff flurry is excellent, especially if you are a strong wizard.
I could imagine a wizard being built this way:
Best: Int
Next: Con
Next: Str
Worst: everthing else.
Forget about Dex and rely upon your magic protections for your AC and saves. Str with a monkish quarterstaff flurry will apply equally to both ends of the staff, tumbling will be a class skill for one of your classes so you will have level+3 as your max; the wizard can do lots of twisty somersaults and poses with his quarterstaff held at the ready.
Cheers