The big problem you’ll run into is that it’s very likely outgoing connections to port 25 is blocked. In my experience it’s very uncommon that residential ISPs allow it, and even most VPS providers will block it unless you request access. So you’ll most likely need some form of relay anyway, and at that point you may as well send directly to the relay.
Still hard to see what is actually sent since it’s all over encrypted channels. To some extent you can look at the amount of data that is being sent and infer from that what might be actually transmitted. Say if the amount of data seems to match what is expected of uploading voice recordings.
For what it’s worth, I hear that Tesla has by far the worst tracking for their adaptive cruise control and auto brake feature, especially after moving to camera based tracking. I’ve owned 3 cars with adaptive cruise control and never had any real issues. Biggest problem was a 2011 Volvo that would sometimes keep tracking vehicles going out in a turning lane, but never braked hard for no reason. Probably your Ioniq will work fine as well.
No mouse problem, but I’ve had to take measures to prevent cat-related downtime. Cats and power-button at the top is not a good combination.
To be honest I haven’t done that deep search into how common it is for VPS providers to block port 25, but in the cases it has been relevant for me it has required at least raising a request and for instance for Hetzner being a customer for at least one month. I’ve figured that it’s a good thing and if a VPS provider has no restrictions at all their IP ranges are much more likely to have bad reputation and blocklist issues.