First, on the seahare, I wouldn't worry about them starving too much. They only live about a year...and so you might get one that is 11 months old (then again, you might get a juvenile one). A big problem is that they'll eat your green hair algae...and poo out the spores. The spores will just regrow...so unless you're doing massive water changes, I don't think a sea hare will help other than aesthetics.
My seahare has done wonders for the green hair algae problem i had in my tank.. Yeah he does crap a ton, but from what i've seen so far it hasn't regrown at all from his droppings. It's been a good month or two since he put in the work on my tank.
Him combined with phosban made my first hair algae problem no sweat! Only took like a weekend and it was pretty bad tbh
Sea hares get my vote! the cleaner from hell..