Thanks I've lots to think about.

You have hit on a current problem my bottom feeders are not getting much or any food due to the greedy oscars. Anything I can do about it?

Thanks for the advise, I will leave out the clown. Loachs.

Is there any recommendations of what I could add as there's still plenty of space even allowing for the oscars growth?

It started as a community tank but evolved, i did have 7 clowns up until a couple of months ago but when i introduced 2 young oscars i had a real bad case of ich which killed off the clowns, one oscar also died and the remaining one was segregrated to recover as some thing had been attacking it ...

That doesn't sound like a good tank to add clown loaches to. They like heavily planted tanks with good amount of decorations, and there are plenty of bottom-dwelling fish already, which will compete for hiding spaces.

Edit: I moved your post, as it's not about "any other variety of catfish", but ...

I have a 180 uk gallon aquarium with
1 Red tiger Oscar
1 albino Oscar
1 Ornate Bichir
1 L001 Gold Spot Plec
1 Ruby Shark
2 Hybrid Synodontis
1 Galaxian Plec
1 Tiger Plec
1 Clown Plec
1 Raphael Catfish

I would like to add some clown loach as i have had them before in a smaller tank but lost them ...