Don't approach Steam until you are at version 1.0 (or at least have a firm release date).
The game I'm working on, Kinetic Void, got Greenlit in the third wave. They're actually pretty cool about that stuff once you're "lit". Our release is nebulously set as Q1/2. The Steam reps don't seem to care.
Games that get released too soon on Steam get crushed (and they should). Developers need to be 100% accountable for the state in which their game is in, and if I pay full-price for a game, I had better get a full game.
I'm fine with a game if it says something like "Hey, our game isn't done yet, but we'll sell it to you in it's current state anyway (for a reduced price, early access, or other cool bonus stuff)." rather than "Oh, and by the way, the game you just bought at $30 doesn't yet have all the features we advertised and is extremely buggy, but we (as the developers) felt that it was good enough to be released as a full game."
I'm still stunned by the complete and utter *** that was Legends of Pegasus.
And with that, I feel like I've said everything I needed to say (and probably more) about releasing on Steam.