That is all in the contracts, which will be negotiated after the contest. The support we will provide is determined by what is needed, and the percentage of the cut is dependent on how successful we predict the game is going to be combined with what support financially we are having to provide.
Remember that at the very least, you get the advantage of our marketing, media contacts, knowledge of Steam and other online stores, etc. And the prize money (which at the moment is going to be around $8,000 for each prize). And if you decide that is all the support you want from us, then the percent we take is not going to be as high as if you needed support with art and music, etc.
Just some truths of indie game development here: most indie games don't even make $8,000. Especially not self published.