I have a PHEV and an older EV (passat GTE + e-UP!) from Volksawgen. Volkswagen’s own cloud service is notoriously unreliable, dirt expensive and even after paying the high annual license, incapable of deivering the car’s State-of-charge reading required for charging automation (such as SmartEV) to work.
As I have WiFi coverage in my car port I came up with the idea to have a Wifi OBD dongle on both of the cars, which could be used to detect the presence of the car and update the SoC reading once in a while (Every 20 minutes or so) to my Home Assistant.
state of charge reading
that is what you had been promising and delivered nothing more than a list of links and thoughts
pretty disappointing and not really worth raising attention cause some people have gotten far deeper.
WiCan is a solution , this dongle you can get from mouser, cause it allows a connection via mqtt to the car
when it is arriving
when it is leaving
when it is charging
BASICLY:
It requires ignition to be turned on (and from turned off after 5 minute the donle will fall into sleep mode)
OR
is charging
In all these cases the car will deliver soc data to HA or EVCC for solarpower surplus charging which is a german open source project (english and many more languages also available). And there you can find such solutions for this particular adapter, also Kia and Hyundai and what not.
You can find that on github and there is also a HA addon to run the evcc app under HA OS.
Most things you have mentioned have been solved but I wonder about your solution cause when I was searching for golf and HA this was a search result even though not much to offer.