Arm waving and headbobbing isnt just a male trait, females can do this too.. it can be an aggression or submissive posture, although aggressive is usually more common. If any aggression does occur, you said you already have a back up plan or enclosure, so really just keep an eye out. I dont know whether a bassie is more aggressive than a wd.. but i know wd's can have all sorts of personalities whether they tend to be aggressive or not. As long as there is adequate space for both of them, you shouldnt have many problems