Amount of o2 to use???

Hi
I want to give my wort a blast of o2. I have a welding tank and
welding valve set on the way to me. I will blast it thu a "sparging"
stone (cintered SS) in a keg ( with hatch open ). What setting should
i be using on the valve??? Do I need to add a flow meter? How much is
enuf?? Thanks for your help.
Gary
PS: Can I post a few Brewing items I have for sale on this newsgroup
without getting the boot???? Is the other brewing newgroup better for
selling???