Step 2: The base.
The holes need to be around 50mm apart to allow the puzzle-pieces to sit side-by-side.
Using the pedestal drill and a 5mm bit, drill the holes about three-quarters of the way through the base. If you are able to, set the stop on the drill to prevent it going all the way through.
After drilling each hole, knock the dust off the base, don't blow it off.
You will, of course, need to wear goggles.