Powers stay with your character, raids are per world and activated by mounting trophies at the original spawn hub. You can progress on one save and use a different one for building, use the dev command resetkeys to remove all raids above the negligible boars and necks, build on an island to cover all possible spawn points, modify the settings with the Custom Raids mod https://www.nexusmods.com/valheim/mods/278 or live in a forest and fill it with tamed wolves which will hunt for food and maintain their own population.