Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
16GB perhaps, as iLife has a lot of templates for its applications. Btw, this question gets asked several times a day.
 
I just deleted Garageband from my new 11 MBA, I probably gained close to 1.8G maybe 2. I also ran CleanMyMac and removed the unneeded languages and gained back 1.6G.
 
You can also reinstall and check off applications you never use. Adding CleanMyMac makes things pretty efficient.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.