Rather than trying to find as many species of fish to house in your aquarium, you're best off keeping the fish in the right shoals. You need some more corydoras, seeing as they like to live in shoals, best keep them in groups of at least 3.
However, kuhli loaches shouldn't give you any trouble in your tank compatibility wise. They tend to hide through out the day, and during the night you shouldn't have many fish bothering them at all. Kuhlis too however, like to be in groups. So if you do believe you have room for them, get a group of at least 5