Hello Yellin,
I'm not a specialist of Proffie, but schematics seems ok.
Be careful that on Proffie 2.2 -> BATT- and GND are bridged by default which might prevent low power consumption in sleep mode when using neopixel config.
Also, how I can safely pre-wire and test the components before assembling everything in the hilt. I'm using a 18650 battery.
Not sure what to answer to this. Clean your desk to avoid shorts by a loose parts or tools, use long cables enough to match your final build and to avoid de-solder/re-solder when you can.
But pre-testing your built before mounting everything in your chassis is the way to go and further more, even during your building:
Test, test and re-test, especially if you have metallic parts around.
Good luck