It's hard to find plecos that don't get huge. Some places have bristlenose plecos that stay small. The problem with plecos is that from what I've read, most of the smaller ones really aren't very good algae eaters.
Even the smaller plecos are still going to get up around 4", and like JustOneMore20 said, it might not be the best idea when you've already got that much in there. You've got aggressive fish, and from what I've seen, aggression becomes a much bigger problem the less space you have, and most fish get a little meaner as they get older.
I have tons of ottos, and I really like them. They actually eat algae. They really don't seem to get picked on too much. They're pretty quick and get away fast when someone tries to nip at them. My panda corys just obliviously root around on the bottom, and they'll let someone come right up and take a chunk out of their tail, but my ottos do just fine.
If you don't actually have any algae, though, I guess you wouldn't really want to add ottos. Mine spend all their time eating algae off the glass, driftwood and plants. I don't know if they'd be able to get the hang of eating algae wafers.