but his life changed when he met a stranger with whom he went on an expedition to the Mountain of the Moons
Why did this boy make such drastic life changing decision? getting hint or direction from a stranger sounds fishy. You need to make better reason for this adventure. Especially if the focus is storytelling and narration.
you cannot buy anything, so you have to also be careful with your resources thorugh your journey
So how exactly could player survive with depleting resources? IOW where and how player could find resources?
explore the areas for anything valueable or rewarding.
Player needs to survive yet they could spend resources to explore areas for valuables?
Last but not least, you need to design the very basic mechanic of your game. Once you got that, the rest will be expanded from there.