I think 12 would be fine...but 10 would be ideal for me. They get big and gnarly in like 8 months, trust me. Your options for more fish are limited, but I'd say a good sized Bolivian ram could probably do just fine in there. Something that can hold its own. I'd lose the oto and add a bn pleco if you're worried about algae. Maybe some nerites instead. That oto is gonna be one heck of a play toy for those barbs.