Ideal run size has been discussed at 150-300 sets of buttons where one set has 4 buttons and 2 knobs (Mk2 and Mk2a). IMHO, the most significant data point was Stu's confirmation that the number was in range of light kits sold to date.

As far as forecasting future demand, I'd peg it at 300 sets. I don't think you're going to be able to get a solid forecast on continued Empeg uptake. If the buttons sellout, then I'd gauge whether a second run is warranted.

I'd second genixia's idea of bundling all colors together for an order for simplicity's sake.