You get a year's free of seat connect.
The Cubic telecom is for in car WiFi, Internet radio, which is a separate subscription.
You can use both in car WiFi and Internet radio without a cubic subscription, creating a WiFi hotspot with your phone and connecting MIB to that ( or your home WiFi if you only want those features in the driveway

)
I have found that system and map updates can happen without a cubic telecom subscription, I believe they are downloaded through the seat connect subscription.
OTA Map updates I believe aren't downloaded in one large 28GB chunk, there downloaded partially as you use navigation. For example you may not have a full street level map of France until you set your navigation to an address in France. To try and force a map update I normally set my navigation to a random address in the UK, and do this a few days in a row, sometimes it works sometimes it doesn't.