Hope you'll post a thread about this process, as it's something that I'm interested in doing, too.
As for the plastic, it's just a matter of getting an edge lifted up and then peeling it away. The perimeter of each piece is attached to the car by 3M trim adhesive tape; it's tough, but not hard to peel away if you're careful. The body of each section is held by the usual plastic body clips...they'll yield if you pull, leaving little holes that will need to be welded closed. This process is really easy, although considerably less so if you're hoping to preserve the plastic.