For those based in North America then I believe at present you have to wait as there is not a North America firmware available yet. However for those in other geographies you can, at your own risk, use the appropriate MX-5/Mazda firmware. Do NOT try to use a firmware from a different geography...
The parts listed above for the hub and cables etc should work irrespective of geography. Please do read the installation guide carefully as there is a preferred order and set of steps you should follow. If you use the Mazda firmware you will lose your navigation (however you now have Carplay so it shouldn't be a major issue). While I don't have formal confirmation I do not believe you can use a Mazda Nav Card as the VINs won't match but I am not aware of anyone having actually tried this yet.
Unless you are a trail blazer or happy with the risk I would recommend people wait for Fiat to launch a firmware, and if you are asking when will this be then the answer is we don't know yet, but go and contact Fiat via their website, Facebook, Twitter etc and keep asking them.....
Congrats to OP, he is the second one I am aware of that has updated their 124.
2006 MX-5 Roadster Coupe - Stormy Blue - SOLD (Australia)
2011 CX-9 GT - light blue (USA)
2019 124 Abarth (USA) - White, Manual, Recaro, Brembo, Veleno Appearance, Visibility, Navigation & Sound, Convenience, Record Monza Exhaust.
Mods: chrome Abarth badges, CarPlay, GENK80A frameless mirror, PTP Turbo Blanket, EC P1-P2 tune, EC V4 intake, EC Intercooler, EC Oil Catch Can, Forge recirculating BOV, alcantara bits, red door piping, led bulb conversion, stubby, MX5Things stuff!