As already pointed out a main concern with feeding these small lizards is that they are usually wild caught species and thus contain parasites.
Over crowding will also be another stress on your copperhead; combined with parasites will equal a diseased snake.
I do understand the appeal of a naturalistic enclosure with several species contained withen. This however is something that needs either to be done 100% or avoided. A much larger enclosure will be needed (consider the bother of crickets on the snake as well.) The enclosure should be large enough were the copperhead will rarely encounter another animal while hiding, as such would occur in nature.
Of course other animals should be properly acclimated to captivety as well.
Good luck 