I'd go easy on the oatmeal, it could gum things up pretty easily. Might want to boil it seperately from the other stuff, and only let it boil for a short time.The great thing about whole seeds (rice, birdseed, etc) is that there is plenty of air between the grains, not really any need for the vermiculite.
However, I went the other direction, a bit more vermiculite, much less rice. Its working quite well.