After all the great answers in this topic, from all these honorable people, I have nothing to add, except to give a humble piece of advice, on top of theirs:

You want to make a game that fulfills you, that makes justice to the game you dreamed of, and yet you know very little about game development. My advice here would be to use some of your budget to pay yourself for some time while you dive into this world. Learn to program a bit, learn about some programming techniques, so you are aware of what is doable these days, and how much manpower does it take to achieve them. Then play around with some engine editors, get to know the workflow of this kind of tool. Also, try writing some drafts of design documents for smaller, simpler games. Even if you don't become a guru in game development, you will have an idea of what is happening and how to control your own people.

It is very hard to lead a big project like the one you want, without knowing (potentially) a lot about game development first. You might end up being just the leader throwing in ideas that aren't doable or will delay or make the project not achievable within the time span. Once you feel confident about your knowledge, and you think you know what does it take to actually lead these programmers, artists and designers into working together to achieve your game, then by all means start it. Until then, I really recommend a self-development phase!

If you skip this part, you will probably have to get someone to lead for you, and consequently you will have a smaller role in the process of making this game, influencing it less with your own ideas because of it.