I do something similar. I add about half an inch of oats and just enough warm water that oats start to stick together, like a loose paste. Then I sprinkle active dry yeast over the oats (about a tablespoon). Then I smear my current cultures over them. I try to have two cultures running at once and I change them once every three weeks (but never both on the same week). I keep them on the second highest shelf on my walls where I can't smell them but I can still reach them. By day four, I have a population ready to feed to my fish. My guppies, platys, and gudgeons go nuts over them, but I got the microworms specifically for the rainbow fish I'll be getting in a few weeks.
Oh yeah, my lid has about six holes in it for oxygen.