I think Swamps and Mountains should be switched

Jumping from Black Forests to Swamps is a huge spike in difficulty and in my opinion would fit more naturally as a later biome.

I think Mountains should be the next biome after Black Forest and should swap silver for iron ores.

Crypts should hold silver shaped treasures and ornaments that could be refined down to silver ingots. Silver weapons are more effective against the undead, so upgrading to silver weapons from iron in that biome feels like natural progression with reason.

The Elder should still give the Swamp Key, to keep as an indicator, but the the power he gives should increase 'natural' resistances to Cold and Wet effects. (Tree cutting should become faster naturally with better equipment and stamina increases.)

Introducing the artisan table and stonecutter earlier can open up new recipes that make sense, like if wheat found in meadows or wheat seeds found in chests could be used for bread and dough early. For which you could use a more primitive oven to have 'baked' goods. Later when the better oven in obtained, foods baked could have 'well baked' tags instead to boost stats/effects. This naturally recycles some food recipes for late game while adding variety. Bigger barrels made with iron and an alchemy station could help prepare and emphasize the importance of potions.

In my experience, mountains have spawned consistently closer to Black Forests. Being closer could provide more interest and opportunity to build and expand home bases more fluently to "stone-age". This could keep players more engaged with their homes and schedules, but also naturally putting them in a position to be more prepared for swamps. After building any project or base, there is always a little lull, and a quick realization of "oh, whats next?"

But wait "I have this key still.."

Exploring. Leaving the grand base you invested in and know as home to sail treacherous Oceans and delve into dangerous Crypts. Having more depth to building and crafting before first setting sail can really emphasize that feeling of worry and excitement before doing so. Also could raise the relief one feels when finally returning to their home base with their raid spoils and can easily dive into new crafting for more adventures rather than needing to chore through building. To me, building wasn't as fun and magical after dealing with stress from the Swamp. That on top of re-preparing made the game tedious at times, but I am a solo player so that could be the difference.

oh and having Wolfs with you in the Swamps could be HUGE for solo players.