SDS based video game Thread

For about 3 years now, I've been writing out the plot for a video game based off the Seven Deadly sins in which the main character is a demon hunter working to become a master in a network of hunters called the Ouroboros Society (No Relations). During the main characters test to become a master, seven grand demons have a sudden and exponential growth in power, because of this, his new test is to destroy these demons. These grand demons will be the personification of the seven deadly sins and each will be in the center of a different realm, and to reach the next realm you must defeat the demon and access a portal that opens after the defeat of said demon. Each realm will have scenery that will complement the theme of sin, like fiery pits in the realm of wrath or a gold palace in the realm of avarice. Along with that, in each realm there will be different enemies to fight that will also be help depict the mood of each realm. Now the way you defeat the grand demons is through a combat system similar to Devil May Cry boss battles(If you have ever played), but you will not be able to completely kill the demon, symbolizing the constant struggle with these "sins" that mankind faces.

Now I have literally a notebook and a half full of just this idea (with much better detail) that have many different possibilities and paths that I could take the concept down, but this is the main idea of the game. I would just like to know if other people found this to be as good of a plot as I do, and if anyone has any thoughts on how it could be improved.

What type of game will it be?
What are you going to write it in?
What skills are required, and how many do you personally possess?

3 years is very long to work out a plot, if you haven't worked out the game!

I want it to be an action-adventure RPG with linear level design where you hack and slash through different enemies. It will be written in C++ as of now because that and Python are the only to languages I really know, and i'm guessing Pythons not really good for game development. I was thinking I would learn to use Unreal for the game, and while searching online I read that I should learn something called Hex. The only skills I actually have complete knowledge and ability of is C++ and Art Design, which is why I plan to go to college to learn more.

Sorry for not stating this stuff in the first post, ive never done too well on forums.