Well obviously it's a bit more complex than that, but I guess in a very general sense yeah, that's all you need really. You can have the files contained in the .exe, or you could load them from the data folder for easy swapping. It's possible to use both ORG and PxTone in the same .exe, but it's easier hacking if you can remove the old ORG engine and replace it with the code needed for PxTone because otherwise there are some tricks you have to pull in order to find room.