Do I have to be a professional / published writer?
You don’t need to be a professional writer to take part (although some are), but you do need to be committed and confident. Committed, because there are no back up writers, and no time to make good on missing sections. If you don’t deliver, you leave a hole. Confident, because there will be only very limited editing done. Topping and tailing if you overstretch your brief and some really basic formatting / spell checking. You need to be comfortable you are able to produce work in a time-pressured environment that you are happy with people reading.