I'm also tempted to put a crayfish in there, but I'm worried about the plants. I've heard they'll shred the plants.
Yeah, those things are like the drunken sociopathic bulldozers of the aquatic world. It'll shred the plants, level that hill, climb out and shred the land plants, kill your toad, kill the fishes, and probably climb out and die in some corner of your house.
Nice tank though, set up looks good, but I think a crayfish would be a bad choice. :/