Great little creatures, very nice, and peaceful fish, when they are stressed, or not feeling to good they will change colour totally to a white/ seethrough colour making them look like albinos.
They definatly like groups, as corydoryus do, but i currently have one on its own at the moment while im funding getting some more, and hes fine.
They do poop like plecostomus's do, from what ive seen, which means they poo quite alot, i dont think the content is too much, but i mean if you had 6 otocinclus, they i guess there would be more poop than a plecostomus of about 6".
They are quite shy fish, IME but do get more confident in time, as do all fish. Also yes there the same as plecostomus's they will eat the algae off the glass on the tank, and also get in some rediculous places, one of mine was always getting himself stuck around the back of the filter between the suckers.
Oh finally they eat algae wafers, same as plecostomus's, but mine will eat the sinking wafers made for the corydoryus as well...
I think that is all i can think of at the moment really...
Cheers.