Not sure about the other fish you mentioned, but clown loaches need to be in groups of at least three, and I have more often than not that the minimum amount of clown loaches one should have is 5 (Shhhh, dont tell anyone but I only have four and they are doing good.)
Clown loaches also get pretty big (in the area of a foot long, if I remember right. Some people, I think in the orient, even eat clown loaches, so they must be big enough for that meal to be worth it) but I can say that my clown loaches are growing at a very slow rate. I have had them for over 8 months and it seems as if they are still as small as the ones I see at the LFS all the time, so if they grew at all, it was a very small amount.
Clown loaches are also pretty shy in a lot of cases and so a larger group of them will help them come out into the open more often.
Also, like I said, I am not sure about the other fish, but I think I have heard that keeping a pictus cat is not recommended if it is with fish that could nip at its 'wiskers'. I am pretty sure they are also able to get large enough to eat other fish and so I would think that clown loaches could become an expensive lunch since they are all mostly bottom dwellers. Again, I am just going back on memory as far as the pictus goes and so I could very well be wrong.
