Your swords will get about 2 1/2 inches each and the zebra danios will be slighly over 1 inch. So you'll have 9 inches of fish in there. If you clean it regularily, you might be able to get away with 3-4 pygmy cories (the other species get too large) or 3-4 otos (otocinclus.) But I wouldn't add anymore for a couple weeks after you get the danios. Danios should actually be kept in groups of 7 or more, but yours should be fine.
