There were changes in how micro-stepping and e-steps are being handled. The original recommendation of E945 was when extruder motor microstepping was 32. That turned out to be difficult for EINSY to keep up with during fast MMU2S filament moves. Since that time, microstepping has been changed to 16 (for 1.8 degree motors)
Instructions in the intro have been changed to match the recommendations here.
Your slight decrease from E473 to E455 is appropriate if your extrusion measurements indicated the need.
Moved gearbox instructions to before main extruder body prep
They are regular M3 hex inside those pockets.
T-Nut refers to the black, delrin nut that rides up and down the Z-screws.
Yes. The filament path insert is ONLY for the MMU2S internal sensing lever.