Do we have to sell on here to participate? If we sell another way then what do we upload here?

There shouldn't be a required place to sell/share your game. You can always make a post with a link to your game if you end up selling it somewhere else.

Yep. Exactly what Arrow said. Since there's no judging or ratings, it's pretty casual. If you want to sell on another platform you can always make a post here to share the link. But it can't hurt to sell in two places at once! Just more traffic for your game!

You could also upload a demo on Itch with a link to the full game, wherever that is hosted. If you have time, of course.

And the deadline is more of a guideline to keep you focused, but if you need an extra week to get your store page up or to add a demo, it's totally fine. 

Thanks for the replies.