Thanks for the great advice guys. I know my question was kind of vague. The main thing I was curious about was how to distinguish game ideas meant for a 40 man team vs ones for a 10 man team vs ones that are reasonable for 1 person.
I think I'm better at distinguishing this through past failures. Games like Grand Theft Auto are more obvious that they need a huge team. MMO's typically require a big team.
But I think I'll be okay to work on my game. It's 2d instead of 3d making assets much simpler. There's practically no animations since spaceships don't really have moving parts. I have the assets already. It's turn based instead of real-time making the physics ten times easier. So I think I've definitely got a game idea within a one-person scope.
The really tough things that I'm worried about are creating a hundred unique skills for the spaceships to use (one hundred is my starting goal), and then making the AI to properly use those skills against the human, and then the toughest thing is making it all balanced. But that's something that is only limitted by my creativity, so I'll have to tackle it!