They should be. =] You don't have to get just one snail or one shrimp either. You can get many shrimp or 3-4 snails, or both.
Also, that swordtail, unfortunately, is gonna get too big and messy for that size of a tank. Can you upgrade, or possibly return him to the fish store, or find a new home for him? If not, then I wouldn't add any more fish. =]
Also, ottos are too active for that size of tank, I would recommend them in a 10-15 gallon minimum, in groups of 3 or more.