Clown loaches and pictus cat fish can easily live together. However, I suppose that there is a little cave competition between the two species. With the application of a proper tank design - in other words, with a lot of hiding options - there are no problems.
In my case pictus cat fish show a remarkable breeding joyfulness.
So far, I unfornuately had no luck in having clown loaches together with cory. After a while, the cory were simply gone. In how far this relates to the presence of clown loaches, I can't tell. Please add your experiences with clown loaches and cory!