This might be a little long, but I feel compelled to share it, because this mindset/approach always been useful to me.
I have a bunch of productive (as in "producing something") and physical skill-based hobbies and one of the most important things I learned is that, the biggest motivation boost I get is from completing small but important tasks.
You have quite an extensive idea, and I can relate to that. It's fun to design a game! And I had been there as well! Originally I wanted to create large point-and-click dating sim. But, it was too much too soon.
Like any other skill based hobby, it's important to start small. Starting big without any background in the hobby you're going for (game dev in this case) can easily crush you when you hit a big obstacle.
Ask any dev here and they will also tell you, they started with simple stuff first, then they put everything together.
So, dont rush with all the big things. Motivate yourself with the small learning process first! This way, you can keep having fun!