Help me MOM'S!

Hello to all you Mamas out there. My friend just had her baby boy and he’s a meager 4lbs!! He’s tiny. This is the friend that asked me to make her a baby hat with a skull pattern on it. I have U.S size 5 (3.75mm) straight needles and worsted weight black wool. I have to knit it flat so I can use one of the charts I was given (by you wonderful peeps). My problem is I know nothing about babe’s and I don’t know how many stitches to cast on. I also have never knit a hat flat so I don’t really know how to do that either. Any insight would be appreciated. The baby is still in the incubator so I still have time to be the first knitted gift. THanks everyone.

This site should help you
http://www.bevscountrycottage.com/preemies.html#p-hats