Wow, I like that! Simple but beautiful :) I can see some very familiar fish species there too :)
As for the crayfish - I usually try to keep a pair but for some reason, there is a way more males than females in most crayfish species so I often ended up having males only. It takes a few months before you can determine the sex. Also, once the males get big enough to hurt one another, they start engaging in pretty brutal fights so it is not recommended to keep more than one male in one tank. But I love them. I have had several different species and they are all fun to watch. A few weeks ago, I posted a video footage of one of my crayfish molting on Dlive :) Crustacean molting is a very interesting thing to watch too.