I have 9 ottos. 4 in one tank, and 5 in another. 4 of them I've had for three years. And 2 out of the three years one lived all alone.
They all eat wafers fine. I've never had a problem with them not eating them. Maybe they learned from the plecos? Thinking that maybe the case I paired the new guys with elders so they can learn. They are not difficult to take care of.
One of my techniques for buying Otos is not to buy them when they first come into the shop. I wait a few months later and then pick them up. (well Ive only done this twice and seems like a good idea to me).
Something I've noticed is that they do not eat that much algae (but have read in these forums that they eat an invisible film that grows on the glass?) But I guess everyones milage may differ.
As far as something to eat leftover food, decaying plants, and 'ふん’. I highly recommend Yamato numa shrimps. They last forever too. I think have 10 in one tank and 5 in another. I have one abeni puffer and those shrimps are essential for getting the bloodworms that the little guy misses.
I never gravel vac. I only change out the water. I asked Amano's guys if they gravel vac and they said, "No, we only siphon out the water". But these are for really heavily planted tanks where you can't get to the soil anyway.