1) If congress wants to justify impeaching someone who no longer holds office to set an example, maybe they should consider impeaching some dead Presidents as well so they can set examples that no one should do what, say, President Nixon did?
2) Under the premise of double jeopardy, once Trump is tried and acquited of inciting, this would presumably preclude any other prosecution based on the same or similar charges at the federal and state levels. I've read about some Democrats pushing for criminal prosecution.