Fitting connectors instead of soldering things together yourself, would greatly reduce the buildtime as well as the number of possible errors.
Looking at the build / assembly:
The wiring is done when the ‘mechanical build’ is complete.
This results in having to solder things that are in an awkward position, or have to be removed / taken apart again to be wired. A critical look at this - esp. the order in which things are done - would improve the build process a whole lot, without any cost!! >> First solder the connection onto an electronic part, then bolt it into place, as much as possible.