Information wise about Satan is that there is a lot of entities have taken up the name even though the name itself is actually a title, the Satan that people refer to is likely no longer a major player in this game of life like almost everyone else so who knows. One of the problems with this world is that it is over exposed to darkness and the dark entities well beyond what had been intended due to past mistakes over the eons. The solution on God's end is to basically close the books on this version and give humanity another chance elsewhere instead of having us make do with it all as is however there are some years before that happens. As for the darkness that was only meant for spirits to have some experiences where ultimately coming back into the light, where it goes wrong is that they get stuck or choose to not return preferring to stay there similar to how people are in this world rather than choosing to go elsewhere with each incarnation. As for reincarnation and Christianity it was a corner stone in the first church however it was removed during the Roman era along with dozens of books from the Bible as well many small changes in the existing scriptures. They didn't scrub everything so there are small hints that are easily distorted to fit existing doctrines. Essentially the Roman church removed a whole testaments worth of material as well decidedly didn't record what was in the oral traditions of the first church for which has been lost with the exception of several dozen books like Enoch ect. My advice is to search for what is and not be constrained by doctrines of the modern church and modern opinions of those in the churches as that puts a lot of limits on spiritual growth.