The display board, stepper, driver, and power supplies are on hand. The question is: wait and see if the developer sells his interface boards, or assemble it the way he did with the prototype, using Ebay bits and bobs (as the Brits say). The parts are certainly affordable; for example, the logic level converter boards and power supply are about $2 each. Because of the very low price, the boards were ordered through Ebay, and if/when the developer starts selling his boards, it'll plug right in. In either case, a kit of connector parts for the 0.025" pins was ordered, so it's covered either way.
The developer used cogged belts and pulleys to drive the QCGB in his G0602 lathe. In Part 11 of his video series, he shows how another hobbyist instead used the existing gears instead of belts. I haven't yet checked to see whether that can work on the TSL-800, as gear diameter (and ratios) will dictate whether that's workable.
On a related note; I have no idea how much torque will be required to drive this whole affair. It's not a straightforward issue because of all the variables, such as: feed rate, cutter speed, cutter sharpness, gearbox ratio, pulley ratio, lead screw ratio, machine rigidity, and probably half a dozen other variables. The developer's lathe is pretty small, and he used a ~230 in-oz NEMA 23 stepper. Suspicious that this might be too small (based upon nothing other than me having a more stout lathe) I went with the next model up with ~440 in-oz. Will that be enough? Who knows!