Phew, that WBS grew quickly when I started creating the document. At this point, it feels overwhelming - how will I ever be able to make a finished game? But I guess that is the journey we all will have to do. The WBS seems really helpful, anyway.
In my game, I have identified three main priorities: Player character movement, Combat (obviously), and Interaction with NPCs. The latter is what I hope will be the core of my game, but it will take some time to implement and, most likely, some knowledge that I do not have yet.