Otos haven't been tank raised yet so they are all wild caught. The trip is rough on them as they are not the hardiest of fish anyway. Usually, there will be about a 50% die-off when they arrive at your LFS. Before you buy them, always ask the LFS how long they've had them. If they've been there at least 2 weeks, you are probably fine to buy some as the die-off should have ended by then.
They are schooling/shoaling fish so you do need at least 3 of them. I have also struggled with keeping otos. They seem to just die for no apparent reason. I finally gave up and didn't buy any more after the last of mine died. My experience was that they really tore into the algae when I first put them in the tank but they seemed to lose interest in it later on. And after I gave them cucumbers for the first time, they all but quit eating algae altogether.