There are no restrictions at all if you do not win a cash prize, so top ten you can do whatever you want.
For the winners, the IP stays with you, but it really depends on why you are making a sequel. If you are making a sequel in an attempt to avoid having to publish with us if you instead just refined the original game, that really is kind of trying to sidestep obligations. If you are doing it because you already published the completed original game with us, then nothing is stopping you, but we would hope that we would have proven ourselves capable enough that you would want to publish with us again :).