octopus don't need a deep sand bed, but they need rock work to hide in, and a very tight fitting lid with some bricks or something heavy on top of it so they don't escape. they are highly intelligent and will escape if they can. i haven't heard of one that ate prepared foods, so you'll have to feed it live.
i don't know the names of the species that stay small. you'll have to do some research on your own. i've never kept one, so hopefully someone else will chime in.
i'm also not sure about the garden eels, but i'm not even sure why you would want to keep them. you could achieve almost the same thing with engineer gobies.