This may seem like such a silly question, but here it is. If you are going to add a flavoring to buttercream (pineapple, bavarian cream, etc.) do you still use butter and vanilla flavorings? Or should they be left out altogther?

You can do it either way. I like the smooth underlying flavor of vanilla, but it does shade white frosting just a bit. If your other flavor is clear and you are looking for white-white finish, you would most likely leave out the vanilla. (clear vanilla does not add the same richness of flavor)