That is it, but (big but) you will have some trouble knowing exactly how much ammonia is being produced. It takes a little time for it to decay, and in the meantime you have kept on adding more, so I don't know how to control the ammonia doing it that way.
You might want to post a new topic about fishless cycling with fish food (or google that and see what you get) and people who have done it might be able to tell you exactly how much food to use for your size tank.
Slate is a great thing in a tank, as it is inert. You can just scrub the heck out of it, pour boiling water over it, and put it in the tank. It is sharp on the ends so you will want to take special care when placing it, as it can very easily slide down from being stacked and literally punch a hole in your tank side or bottom. I have a feeling you might have some trouble finding egg-crate (white plastic grate sold in the lighting department to cover fluorescent fixtures) where you are, but that cut to fit the bottom of the tank, is a great way to protect the bottom from rocks and such.