The multiplayer should just be one mode where you can decide to trade/team/raid other players and the creative mode wouldn't be fun I think there should be a building mode where you take no damage and don't starve or dehydrate but you have to get your own resources outside of building mode. Building mode should be turned on and off in main menu and in game toggled with the buttons 'ctrl b' in game. You shouldn't be able to do much in building mode apart from opening chests, building and breaking. In building mode you don't get resources back from stuff you built if you break it.