I wouldn't add the otos for a few months or more, they need some established algae to feed on. They can be finicky eaters and won't always eat flake food, sinking pellets, algae wafers, etc. They, as well as a bn pleco, would enjoy some blanched zucchini or cucumber occasionally, and lately I've been feeding them Repashy. (soilent green) And I wouldn't worry too much about adding a bn pleco with your plants, although one of mine used to torture a sword I had.