Personal experiences --
I've had/have crayfish of the cherax and procambarus (Hammer's Cobalt Blue Lobster) genus. The cherax was an absolute monster. He wrecked my filter, threw the driftwood around and ripped up all the plants. Never again.
The procambarus lives in my son's 65g Silver Dollar tank with a school of rasboras, a school of rummy nose, two SAE, and six silver dollars. Before that he lived with three of the aforementioned dollars, two tiger barbs, a pleco and a snail in a 20g. It was very crowded in there.
I have never had a problem with him. Sure, sometimes he'll move plants that are in his way, but I made sure I planted the 65g so that he can have room to manouver. Crayfish can't bend their bodies, so you have to plant smart.
The Silver Dollars are not afraid of him, even the smaller 3" ones. In fact, they steal his food right out from his claws. I feel sorry for him sometimes. The other day I watched Silver and Baby Silver do a tag team on him. Silver distracted him while Baby swam right between his claws and grabbed his wafer. I gave him another one. He rarely raises his claws at anyone, even the rummy nose and the rasboras. They steal his food too.
He's never bothered the pleco. They often sleep in the same hidey hole. I don't even think he knows the snail is there.
He's pretty cool.
Roan