Clown loaches are fine in a 75g, as long as you realize that they will eventually need a tank that is around 6 ft long. If you are able to provide them a tank that large in the future, by all means get 4-5 of them now and let them grow in your tank.
Aislinn, I am like you in that I don't buy fish that I know will outgrow the tank, but many people are not like us. As long as a person realizes that a fish will outgrow their existing tank and can provide the proper housing for them in the future, I see no reason why they can't get that fish now.
As far as cories and clown loaches go, I've never kept them together, but I do keep Yoyo loaches together, and while they aren't the same fish, they are both silly loaches. My Yoyos don't bother the cories and the cories get their share of food. The loaches are more active and voracious at feeding time, but I put enough food in the tank at night to ensure that they all get something.
I can see how a large clown loach could outcompete cories for food, being that the are larger, but I don't see them being aggressive.
Maybe someone who has kept cories and clown loaches together can provide some input. I know someone here on AC has to.
