I don’t know the answers to those questions. Honestly. I do believe satan exists, and I think there’s ample evidence in the evil we see around us everyday and from a historical perspective. There are lots of questions regarding religion that we simply don’t know the answers to, and probably won’t until we die. That doesn’t mean that the devil (or God for that matter) doesn’t exist.
Some things have to be taken in faith, and if you don’t have that, then nothing will convince you anyway.
I do have faith I believe in god though not in the same way that many do I think. I’m just not convinced in the devils existance as a tangible entitiy. I think humanity has a great deal of good within itself and a great deal of evil. I’ve felt the presence of god a few times in my life whether he tips the odds slightly in my favor or gives some insight which helps me overcome an obstacle. The only evil I’ve ever felt is from within me.