Booted TotK again, played for like three hours. After using a guide to find Hestu (east is not a sufficiently specific direction to give from the western half of the map for something that important) we finally upgraded our weapon slots.
Also learned water can freeze, and if you merge a weapon with ice, you can make more ice. That's fun.
Oh and the hovercraft prefab doesn't float very well, but you can kludge it by pulling the stick right back so the fan pushes you up out of the water, which has the bonus of making it look like it's going very fast in a cartoonish way, and control about as well as that implies.