Ok - cleaned up the wiring a bit and kept going. Gasket reduced noise significantly and a bit more current to the motor (replaced 100Ω resistor on motor on.off with 27Ω) make dispensing quicker. I'll post a video. In the meantime I've updated the schematic in the gallery.

One thing I still want to improve is detection of coins/washers and black plastic bottlecaps. The way I had the deposit sensor positioned, flat things would falll with the edge facing the sensor. Sometimes the sensor would miss them. I moved it to a 45°-ish angle so it would cath this more often, and this seems to work a little better - not perfect, but better.

Black plastic bottlecaps also go unnoticed by the sensor sometimes. They usually have some logo/writing/dirt on them, but you can still catch it at the wrong angle and miss it. I'm thinking of adding a secondary sensor on the drop chute at a 90° angle to the existing one to try to catch this more often, but I think I'll wait until I test it more to add that complication.

I ditched the battery level meter - things were getting crowded in there and it's probably not really needed at this point.

So for now, it's in a testable state. Now to find a good spot for it. No shortage of crows, magpies and jackdaws in Amsterdam.