Personally I would prefer the competition to start during the summer. Many of us possible contesters are students and don't really have time before.
I then wouldn't mind if the contest lasted about 6 months. This would allow you to work on and off on your game. We all know, that sometimes you just don't have the time or energy to work on your game, and I don't think people should be punished for taking a rest and charging up the batteries.
If you insist on having stage deadlines it should be the competitor who decides what the deadlines are for his/her own project. And there should be about a month between each deadline. But I don't think that people should be scored on how well they succeed on adhering to the deadlines. The deadlines should only be there to help us all through the development progress.