I would say in a 55G the Flasher/Fairy wrasse family is the best option. Probably the most jumpy of the wrasses though. You can do a couple leopard wrasses as well but those are considered "Expert" fish, although the term expert can mean a lot of things. I think in the terms they are using it means your tank is well established and you have a firm grasp on the requirements for the fish.. other than that there isn't a whole lot you can do other than try and cross your fingers. Stay away from Coris wrasses, even most Halichoeris can be a little on the agressive side compared to flasher and leopard wrasses.
As for a guess on a total.. I would say 4-6 wrasses in a 55G if they are suitable tankmates.