The order to build in

Sequence

1. Stabilisers into the PCB first. They are far harder to reach once switches are in, and they are the part most likely to need redoing.
2. Test the PCB. Short each switch position with tweezers and confirm every key registers, before anything is permanent.
3. Plate onto the PCB, then switches through the plate into the sockets.
4. Check the corners. A switch not fully seated will bind or not register.
5. Case, then keycaps.

Why testing early matters

Finding one dead position after soldering 80 switches means desoldering to reach it. Finding it in step two costs nothing.

The common mistake

Fitting switches before stabilisers. It works, right up to the point where a stabiliser rattles and the only way to reach it is to take the board apart again.