Wow this is a hard question. I don't know how you are going to manage getting enough right away, so you might have to supplement with formula.
If you think you have extra milk after feeding him, pump the rest out and save that, plus every time he would have to eat and you are not with him, pump your milk and give yourself about 30 minutes to do it and what you get is what you get. It will be harder to have let-down for a pump and not being around the baby will make it harder too.
I would say that you should have at least 3 ounces to give him for each feeding. If he is not finishing all 3 ounces after the first few feedings, then you can start backing down.