Everyone has pretty much made the right point already, but just to put things into perspective.
You're talking about a free roaming adventure game with multiple story lines. My Managing Director used to work for Sony Entertainment and he recently brought in a design document for cancelled project. This game was intended to be in a similar style to Tomb Raider or Uncharted, a linear adventure game with a single story line. The design document was over 500 pages long and covered everything from concepts, level design, game mechanics the lot. This took over 18 months to put together and the company pitching the idea went bust before they could even start production.
Hell, look at Black Mesa. No sign of a release date after 7 years and over 30 developers who already had the tools available to them for the most part.
You NEED to start out simple. Daubeh's mention of Minecraft is a perfect example. Notch created what was essentially lego which could be played online for free, then he added the survival mechanic and kept building onto it. Now he's a millionaire with his own company which has multiple members of staff. (BTW don't ever get into an industry for the sole purpose of making money because that never works. You need to have passion, but it's obvious that you have plenty of that already. Just east off a bit
)