I'm getting ready to launch the FTFC in the next day or so, and the timeline will be starting now and ending in January. The goal of the challenge is to promote learning, designing, and research - not to solve a particular technical objective, but to encourage, teach, and enhance people's skills to promote the hobby in general. So if you want to start before I get the official post up, that's fine - and anyone who has an in-process project that qualifies can enter too - and it's perfectly acceptable for more than one person to do the same plane/plans, and for one person do to more than one entry.
No size or scaling restrictions - build, update, modify, adjust, scale, etc. to your heart's content - as long as you have a picture of a balsa plan to share with us for the model you're building and talk about all the cool things you're doing to make the foam board version of the plane, it's all good!