Start new game. Load trainer. Only use the easy kills option. Run through the main quest exclusively using the bow (one shot kills everything). Don't pick up any items unless you have to. Don't buy anything. Complete hunters hunted and coming storm quests in main quest line. Then play as otherwise.
Can report: encountered same bugs on first play through. Second play through, stuck to only main quest, used only easy kill turning it off before each major interaction (Any meeting with arthr, the ettin and arthr, Gnash, and the High King)and made to complete the coming storm with no issues.