Extrapolate from what's established,

especially with things that strike you and the players as odd or anachronistic. The villagers don't fell living trees from the Great Wood. How does that affect construction and tools? Do houses have doors? Where do folks get wood for spears, bows, and arrows? They can't fell trees, but can they coppice them? Decide for yourself or (better yet) ask the PCs!

It's okay to change or ignore things. Exploit the setting guide, don't feel constrained by it. With that said, think about what you're changing and what ripple effects that change might have. Little details (like swapping Stonetop's whisky for mead) are safer to change than core assumptions (like the village's egalitarian culture).