As others have stated, I'd pass on the aro. Finding decent sized clowns to combat the fast growth of the Oscar could present a challenge. Mid-large clowns aren't always easy to find. I kept clowns with an Oscar in the past. While he didn't outright attack them, he was aggressive enough to make them hide a lot and change their outgoing nature that makes clowns so great. From my experience, I'd suggest looking at a more relaxed cichlid such as a chocolate, severum, uaru, geophagus, etc. As far as the BGK, you may want to get him before the clowns and get it eating well before introducing the clowns to ensure they don't outcompete it for food. While I have no personal experience with them, I have seen people keep monos in freshwater. But it is my understanding that they do best long term in brackish. Something else to keep in mind... Many clown loach keepers get addicted and add more to the shoal than they first planned. They are very social and do well in large groups. That said, six is a decent number to see their social behaviors.
