Yep. The answer will be in a spoiler segment.
Keep him and Linos as your ‘guests’ during the winter. Assuming you don’t kill him for something else, he leaves during the following spring.
No; you have to do different combinations of stats/activities to get all the achievements. Some things won’t work, not unless you cheat.
Unless you cheat, no. The author has stated in the future expansions, you may well do so.