I have a couple of single species towns and you have to remember that there's only a certain amount of squirrels in the game and if you let too many of them move out,then you'll have a mostly squirrel town and not an all squirrel town.I learned that lesson from my mostly duck town.Other than that,Ricky is a fairly rare villager that I don't see in many towns and he seems a bit hard to find so if you really like him,then you should grab him.I currently have Sally and she's been great but I could see you not wanting three normals.