Using the drill press, drill 3 or 4 holes for the registration dowels. Make sure they're located well to hold the parts together.
Mark these first two pieces as your template. To use the template to generate an identical slice:
1) Drill the registration holes through first.
2) Drive short dowel segments through the template and the new slice
3) Rough cut the new slice on the bandsaw. Make sure not to gouge the template, as it will affect all future slices!
4) Clamp the template piece and new slice to the workbench, and use the router flush-trim bit to cut both pieces identically.
5) Remove the new slice and repeat until you've built up the full thickness of the mold. Apply wood glue between each layer as you stack them together on the longer dowel sections. When they're all in, Clamp the mold together while the glue dries.
6) Scrape any excess glue from the mold surface. It must be completely smooth!