Comatose:
I have a dream of making a massive game, like you. I get the passion you have. And since you have said you are putting this project on hold it seems you are willing to learn and adapt with hurdles that come your way, which is pretty awesome in my opinion.
I want to throw out some thoughts to consider. I am not saying you can’t achieve this, or you should give up. What I’m gonna write starts out kinda negative sounding but I promise the end is much more positive!
You said you are an artist. I am an artist as well. 
Let’s pretend someone came up to me and said “I no basically nothing at all about art, but I have a vision of this amazing mural in my head, and for the next 2 years I am going to draw it. It’s going to be super detailed and a massive under taking, but I’m dedicated, and I wont stop til its done.”
If I heard that I would imagine this person setting out with his/her mural design. But then they learn about art along the way, or they look at what they’ve done, and not like it, or run into problems. This would lead them to learning about composition, color theory, and proper anatomy. So they forge ahead. But as they learn, they realize they should have set the mural up differently. They’ve already drawn some people in the mural that don’t look right. The farther the get in the mural, the more they want to redo to it. Maybe 6 months in, they stop and realize, the mural is too sloppy and the quality in parts is too low for them to ever achieve their vision, so they scrap it.
So, after I imagined that in my head, my advice would be that if they really have this passionate vision and they want to make this beautiful mural, then they need to learn the fundamentals of art and get some experience. And the same is true for you - I believe before you finished your game, you would have learned so much that you would decide to scrap your project or TOTALLY revamp it. Instead I would suggest learning much more of the basics.
See, I told you the beginning is negative! And, you already stated that you were putting your idea on hold, so if I was just saying that, I would be an A@@hole!
Now for the positive feedback.
I think you SHOULD work on your game, kind of. Watch this:
I think you should write up a GDD for a very small game (not to sale, just to learn, and to eventually demonstrate to others an idea of what your game would be like.). Like, one small level. It would be a small taste of your dream idea. So I am going to spitball here a bit, since I don’t know much about your idea. I’m gonna say you want something like:
^— So something like that, but that fits better in your world.
So bam, you have a simple game to make! But its going to take a long time, since you are inexperienced. But, the time you spent wont be wasted, because much of what you will learn doing this small game will help you greatly when you make your bigger game.
Then, making your game. Follow these steps:
- Make a list of every task you will have to accomplish: NPC/ogre/main character/cat models. Environment. AI. Music. Animations. Combat. Dialog. Etc.
- Cut everything you can. If you finish the bare minimum, you can add in other stuff. That means cut the music. Cut the NPC. (Write a couple paragraphs the show up at the beginning of the game). Cut the choices down to two.
- Figure out which things you don’t have to do yourself. (there are free graphics out there for a natural environment, same with a model for the main character, ogre and cat.) Basically do everything you can to cobble together this game as simply as possible.
- Rank the remaining in order of absolute importance.
- Start making your game!
If you get this far, you might get stuck. Maybe you don’t know how to make your game! If that’s the case, put your simple game idea on hold, and learn. Here are a couple of tutorials on making the very basics of a 3rd person game. Do those. Do other tutorials.
- Make your game! If you finish your very simple game, you can then look to your big dream project, and re-evaluate how you want to tackle it, with everything you’ve learned. If you don’t finish your game, because you get stuck, and you are in too deep, then put the project on hold, and start out smaller. Make a Pong clone, or an Asteriods clone, or just keep following a bunch of Unreal tutorials until you’ve learned enough to make it.
Here area couple more videos I would suggest watching. (not tutorials, just short videos about making your first game.)
Ok so maybe you are thinking: “I cant make this game myself, of course. I don’t know programming, or 3d art etc. But I am going to get other people to do that stuff, so it’ll work out. Plus, I am going to learn it as I go, and get help from the people I’m working with!”
Well, my response to that is in my next comment, because this is getting too long!