Start with just a little, maybe 0.25 or so at the end your run if it's comfortable enough to do it. Don't overdo it the first time, even if it feels OK. The real test will be walking around the next day. Pay attention to how your feet feel. If they're really sore, you'll have to do less BF next time. (Not the next day. Don't do BF running more than every other day when you're first starting out.) If they're a little sore, but not bad, you did about the right amount. Do the same amount every other day until you hit the next stage. If your feet feel great the next day, you can safely do a little more the next time. Give yourself plenty of time to get used to it, and to get comfortable with your new stride if it changed.

+1 on this.

I can just go out and do a 3-4 mile barefoot run and it feels great but the next day (and for several after that usually) the tops of my feet would hurt pretty bad.  Those muscles are small and very easy to overtax when you are starting out.  Hence the reason I have had to restart a few times 

I tell people: go barefoot, on a hard smooth surface (bike path, e.g.)... when you think "Maybe I'll just do a little more" STOP!

You will, no doubt, overdo it at least once in your first 5 runs. But once you do that once or twice, you'll learn to listen to that little voice and STOP.

There's also a good chance your calves will be sore after your first few runs... let them totally heal before you go out again.

My $0.02