You should only need one character BP. It can have its skeletal mesh set to whatever you want it to start out with.
That event you made, To Outdoor Character, in your MyCharacter BP, will work just fine. Cast to MyCharacter instead of Cast to MyCharacterIndoors. From the castm drag out the blue pin and type in the event name. Find it and hit enter to use it.
And then of course, create a To Indoor Character event in your MyCharacter BP and have it fire on End Overlap
Let me know if you run into any trouble