So, I went a little low tech, but it works.
Start by stripping everything off of the front of the playfield. Then tape sheets of paper to the board, edge to edge, being careful to match the edges and corners perfectly. Once it is all covered, make a rubbing of the surface on the paper with something. I used crayons. This will catch all of the important details, like holes and inserts. Number each page and add horizontal and vertical alignment marks(straight lines that cross the paper boundaries). No special scanner needed.
Once you are done, carefully cut the tape and scan each paper in(watch for misalignment). Stitch together in an art program and now you have a map of every feature on the playfield. Make this scan into a single layer and use it to generate the final table. That method will be highly dependent on your art program and how the sign printer wants the files.

Additionally, I don't plan on clear coat. I just cut my own version of a playfield protector.