Very light planning is fine. Having a general idea of the story you want to write, and sketching ideas for assets beforehand is all good, but the good news is that you actually have 10 days to make the game!
Thank you for the response. I'd like to be able to just draw rough sketches of the story / progression. Would I need to share and document planning-process as a dev-blog?
Sorry for the flurry of questions! I'd like to also plan the code/components on a kanban board - is that acceptable? I am very new to Unity (but not programming) and I figured if I could just get everything visible, I can also figure out the relevant Unity components I need to learn.