JoeJ said:

RoleRacingGames said:
Undertale, Diablo 3 and Kingdoms of Amalur all fit into the casual RPG category.

I see our definition of ‘casual’ differs, which is normal across people. But i still think you have conflicting interests eventually. Here is an example:
Personally i have no interest in cars and related technology. But i've played Trackmania for thousands of hours over years, because it's a very casual game. It's simple enough i could play it with my wife in splitscreen while talking about the day, and having some fun along. There is no progress system either, so you can just stop playing at any time. No need to deal with save games or anything.
Contrary, if the game had features like tuning / upgrading the cars, i would not have played it. But a friend who does like cars a lot would be more interested.

What i mean is that you have to make a choice on who is your target audience, and serve them specifically. This seems more niche and less mainstream, but it can give you a better base of players. They pick your game over others because you serve their interests in detail and with care.
If you try to go mainstream, serving and attracting everybody with a streamlined RPG experience, then you compete with AAA developers with only little chance of success.

RoleRacingGames said:
I want to set a template for this genre of racing game and hope that someone else comes along and does something even more with it. That's it

It sounds you work on a design document for a long time, making it perfect on paper, and then hoping somebody will join or fund you, because the design is good?

Won't work, because this puts you in the role of the ‘idea guy’. Nobody will take you serious, because ideas are nothing worth. Everybody has ideas. You need more to convince people, to distinct yourself from all those countless idea guys dreaming about big games.
You should work on a prototype instead just design documents. It's much easier nowadays, because there are game free engines ready to use. This saves you decades of learning and work, but it also means there is no more excuse of not working on a game yourself. After that you have some experience on development and can contribute more than just ideas. If you can show a working prototype good enough to show your game is fun, it's easier to get people on board.

That's just my opinion, but if you seriously want to make a game, there is no way around doing it for real. Design alone does not make a game. And without a game, design is not even enough to describe such hypothetical game.

“Personally i have no interest in cars and related technology. But i've played Trackmania for thousands of hours over years, because it's a very casual game. It's simple enough i could play it with my wife in splitscreen while talking about the day,”

This seems to be about the… driving gameplay? Sure, that is also something I intend on being as welcoming as possible.

I'm talking moreso about the story

RoleRacingGames said:
Okay, you could very easily go through a game like, IDK, Forza Horizon 4 not upgrading your car and just buying a faster one in order to progress

Oh, i thought it's mainly about ‘car fan service’, and RPG elements like skill points would likely affect car tuning (better suspension, nitro injection…), and instead cosmetics like characters skins you would offer custom spoilers or car paint.

But that's not what you have in mind, which i only realize after reading your whole opening post as well. What you say makes sense to me, but i'm too much of an RPG noob to add something on that.

RoleRacingGames said:
like I said, I don't plan on doing this seriously for years

Then i got you wrong here too. But making a game usually is a process which takes years of course.

RoleRacingGames said:
what engines do you suggest for a racing game with the elements I described?

Personally i do not use game engines, so can't give good advise. But i would look at Unreal and Unity in that order.

While i write gfx engine things myself, i do use a physics engine. And regarding car simulation i saw a very nice car model in the Newton Physics engine, which is my choice because of high accuracy and robustness other engines lack.
Car simulation really is it's own challenge, and the default car models you'll find in U engines are surely not on par with games like Forza.
Implementations differ a lot here. For example, in Forza they may run a very detailed simulation with hundreds of timesteps per second.
In a game like GTA you likely can't afford such cost, and 60 timesteps per second have to be good enough because there are too much other things happening as well, like pedestrians, shooting action, etc.
The car model of Newton seems a good compromise between those two extremes. It does not require many timesteps, but still gives a very realistic simulation.

Unfortunately it is not easy to integrate custom physics engines like Newton into off the shelf engines like Unreal or Unity. If you use them, you likely end up with tweaking their built in car models to your needs, which may be good enough or even great, but in the worst case you need significant changes or improvements.

So it's surely not easy to pick the proper engine for your needs. But if you have no programming / development experience yet, that's not your first problem. Anything you learn about using engines, doing some programming, or creating and dealing with content is useful. Just keep in mind the simulation topic might become a problem at some point, forcing you to switch or customize engines, hiring a simulation expert or become one yourself.

RoleRacingGames said:
This seems to be about the… driving gameplay?

Yeah, Trackmania is the best car game ever made imo. It's not realistic but just fun. I don't like realistic car games, because this would require a proper sense about acceleration, which we can not deliver with just 3D graphics on a screen.
So when i try to play a simulation car game, i'm mostly angry, thinking: ‘Why wtf didn't i get the curve again? I was not driving fast at all!’
I guess the audience for such arcade style racing games is bigger than for accurate simulations, but not sure.

Regarding your world design - what's your plan to implement the story elements?
The primary question is: Just 3D cars, plus still images of characters and scenery for story telling?
Or full blown 3D characters, with ability to walk around freely at street and interiors of buildings, including motion captured cutscenes?

For the latter, my estimate of half a billion was no joke. So if you present design ideas, you need to tell such things first, otherwise it's pointless for others to imagine and discuss your design based on guessing.