I am trying to think how I could use a router to mass produce the 16 rectangular holes without wielding a hand saw. I have several bearing-guided, router bits which might work with a suitable template. Oddly enough I have never made or used a router template until now. Previous attempts to cut the holes with a coping saw were rather 'clumsy.' Requiring considerable coarse filing to smooth things out but left ragged edges from the birch plywood splintering.
I ended up using heavy brass plates with added barbel weights and G- cramps [C-clamps] to "box in" the router base plate as I cut each rectangle. An initial small drill helped to 'sharpen' the rounded corners left by the 1/4" 6mm router bit. Next time I shall make a square base plate out of Tufnol or plastic to better confine the cutter. The rounded base of the Bosch router does not slide perfectly straight against an edge. Nor does it work well inside a template.