Considering a mimic zebra octopus

I mentioned in another thread I'm building a 55 gallon refugium in my basement. While we where getting the pumps at the fish store we notice a zebra mimic octopus and well.... we really want one.



The plus side is since I'm building the tank my self I can do what I want.



What size holes can I have in the separators if we decide to get one of these?