Very nicely done! is that #25 chain in the reductions? If the ESC you chose survives, great. If it fries, you may not need a higher amperage (and more expensive) ESC. Its possible the same ESC with one added power-input capacitor would smooth-out voltage ripple (which can cause voltage spikes higher than system voltage). Many 12S users have had good luck with this $2 50V capacitor. https://endless-sphere.com/forums/viewto ... 45#p382837
I noticed that many bike frames today have an odd-shaped down-tube, but seat-tubes are consistently round, and with only a few diameters of tubing used. That means this design is very transferrable to other frames. Also, since this design is easily accomplished with garage-level tools, expensive machine shops could be avoided. Bravo, sir!
edit again: I haven't used my taps since I started using steel nutserts, drill a hole in the aluminum plate, slap in a steel nutsert with a smear of JB-Weld, assemble parts so the screw will hold nutsert in perfect alignment while it dries.