I did the retrofit of FSC on my Mazda 3 2018. LKA, High Beam control and SBS/SCBS works fine.
Instead of changing the windshield I used the mounting bracket of a Jeep Grand Cherokee 2018 (it uses the same FSC, at least physically).
For the Wiring harness I found the connectors on mouser electronics.
Bracket
https://www.mouser.com/ProductDetail/538-34824-5126
and the pins:
https://www.mouser.com/ProductDetail/538-560023-0421-LP
calibrated the FSC using dynamic mode using IDS.
when I installed the new FSC i got a DTC coming from the RCM module, so I used the asbuild of a FSC equipped car and change the RCM as-build.
Also bought a new ABS module and ABS pump, but later found that its not needed that the factory ABS pump works as well as long as you use FORScan ABS Relearn function.
I hope this could help you on this quest.
Let me know if there's anything I can do for you since I did this like a month ago.