Ok. Diastatic power refers to the ability of a malt to convert starch to sugar. Flaked oats (quaker) by themselves are not malted, and have no ability to convert. So, if you are using flaked oats, then you need to add in some barley malt or wheat malt, or rye malt which will supply the enzymes needed. 1 lb. of malt per lb of oats should be more than enough. (Same principle if you use corn or rice).
By the way, if you haven't read John Palmer's 'How to Brew', I would strongly advise it. There's an older on-line version that while a bit outdated, is still good to learn the basics. But I would counsel to pick up a hardcopy, read it, study it. It will become your brewing bible, and a reference to go back to, time after time.