So let's bring things a bit more up to date. I have painted the glass cover, cut out the area for the oled screen to shine through, installed the capacitive touch film, installed the oled screens, and am beginning to embark on wiring it all up. With that spoiler, here's what I actually did:
I printed a full scale template of the areas to be cut out on paper and placed it under the glass as a guide.

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Since there was a bit of a trick to getting clean edges (explained later), time was a bit limited and so the screen was painted in thirds using the paper guide as reference.

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After the paint was no longer liquid but, critically, also not dry (also explained later), a self adhesive vinyl version of the template was placed over the top to act as a cutting guide and structural support during paint removal.

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The areas where the OLED screen are to shine through were cut through the vinyl and gently peeled away from the glass.

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Details:-
I tried various methods to get a perfect clean edge on glass including masking tapes and spray paints of numerous qualities and types with very little success. The method that eventually worked used Valspar (UK version of Platikote) brush on quick dry enamel paint. Additionally I also used a Silane glass primer to prep the glass for the paint, however Alcohol wipes would probably work just as well.
Steps:
1. paint on a thin later of paint and quickly dry it using a hot air gun on a medium to low heat (a hairdryer would probably work).
2. when the liquid shine has gone, paint on another layer at right angles to the original brush stroke, then dry again as above.
3. repeat this a few times until you have about 6 layers and no light can be seen through the glass.
4. cut out your shapes with a very sharp knife or scalpel.
5. leave overnight to dry off some more, and repeat the above for the next two thirds.
Because of the rapid heating of the enamel, the paint does not dry properly, becomes stretchy, and most importantly becomes very easy to cut. However, since the layers of paint are still quite thin, it is necessary to have something on the surface to aid the peeling from the glass as the paint can stretch and tear easily.