If you think that is all it will take to make such a game you are seriously underestimating how hard game design is. It took a team of dozens several years to make mass effect.
You can do it, but you have to be realistic in what it is going to require to take your ideas to completion. And you are going to have to find extreme amounts of fortitude to keep going over the years.
Prototype your game using premade stuff. Get the gameplay down and pull in help here and there as you need it. When the game is basically feature complete, build a team to finish the areas you couldn’t handle.