The oatmeal stout is a partial mash and here are some directions
. If you have a bottling bucket, you can pick up a nylon bag that fits the bucket at your LHBS. Use those if you're working with a really limited budget like I was.
I have started my primary off by putting my cooled wort right on top of a primary yeast cake with success but I've found that its better to put it on top of a secondary if you don't use a hop bag or if your primary was over 10 days. Either way, yes the fermentation will take off like a rocket.