No to the clown loach. Like all loaches they do best when kept in groups and those guys get to be 8-10 inches long at least. So a 75 gallon is really needed.
Khulies will go fine in there, especially if you add hiding spots like plants or decorations. They would be the best choice for that size tank as they work best when kept in large groups. The smaller the group the less chance you will see them as they will hide most of the time.
Another loach chocie would be the zebra or the yoyo loach. Both also stay relatively small.
Be aware that loaches will eat or harrass all snails, even the big apple snails aren't totally safe. If you hate snails then that is great. If you like them then it is bad.