Since you're already fluent in Sabermetrics, and your background in sports simming sounds solid, I'll offer this perspective...
It's all about the interface. This game is so deep, rich, and detailed that anyone with a passion for baseball, sports gaming, and numbers will eventually hurtle towards its event horizon and buy a copy.
- Take some time to familiarize yourself with where things are, what things do, and how best to navigate the daily stuff.
- Read the online manual to help familiarize yourself with the simulation specific terminology. It will help you understand the game mechanics, and how to interpret each term.
- Post any and all kinds of questions in this forum, and read the other forums as well. The membership is serious about this game, and has always been helpful to me.
- Start simple, leaving many of the daily responsibilities to the manager/minor league managers, etc if you want to just go in as the GM.
- Play around with a simple league and go nuts, trading, promoting/demoting/etc. to get a feel for it.
- Play around with the rosters, moving guys around to see how they react.
- Finally, it may appear daunting at first, depending on your sports sim history, but the learning curve can also be short, so keep at it.