As a fellow knitter I completely agree with "as much as you possibly can"!
When I was first starting out I decided that I was going to make at least 20 of each type of item; 20 beanies, 20 scarves, etc. I didn't always make them all, but it was a good goal for me. You don't have to do 20, but choose a number you like and shoot for it! :)
On a side note, you REALLY need to raise your prices! Especially on your beanies and scarves, those need to be almost double. I know what that yarn cost you and how long those take. And you're work is really good! Yeah, your beanies should be $40, and scarves at least $60, and headbands no less than $20. I know it's scary to charge that much more for things, but trust me, people will want it more if it's higher priced. :D