The main character (Euca is his default name) isn't really going back in time, it would make more sense to say time is starting over. He can't remember anything from any of his other failed attempts.
The remnant cannot be killed as far as we know. Euca grabbed it by the throat and slammed down in the street when the fire started and it just kinda sat there watching him. Halley was able to destroy it, but as you can see during the restaurant scene, it just comes back a short time later and picks up where it left off. According to Echo, wishes can only die when the person who made them gives them up. Echo did kind of lie though, because it looks like wishes can also die from resisting their purpose, which Halley said is what is killing him.
As for who created the Remnant, I won't spoil it, but all the pieces are there for you to figure it out. Replay it and pay very close attention to both dialogue and the artwork of the characters. Jenny also dropped a big hint somewhere along the way.
It's actually better for Sissel to stay there in the woods sometimes. Even with his old house as run down and broken as it is, it's what he called his home for several years. It's one of the few places he can de-stress and it's close to the lake where bradley is. He really should get better at swimming though.
As for Sissel's attitude toward money, he doesn't have a problem with having money, he just doesn't want to be a nuisance by relying on everyone else. He also probably doesn't want to exploit anybody, since that's the thing that caused the mess he's in to begin with.
Edit: I was wrong, it laughed when Euca slammed it down, which is just a little bit more creepy. Halley also said that her destroying it came at a heavy cost, which she later reveals. Everyone agrees that Halley is incredibly strong, but she has to make a bit of an unfair sacrifice every time she does something, therefore she isn't a permanent solution either. #3 also tells me you are going to like owens route.