The night mode you found is the only dark mode. I thought I wanted a dark mode too, but after having changed manually to night mode in the day I realised that it doesn't really work well for a screen that can be in direct sunlight and difficult to see. It will switch to dark mode when it's dark, tho.

It sounds like your test vehicle had the FSD package as that includes a feature where it will chime when the light turns green and you don't go.

I personally haven't got much experience with blind spot monitoring systems...my Model 3 is my first vehicle to have it. I do find that the visualisation can be a bit too zoomed in sometimes that you can't see all cars around you on the screen. However, if you pinch to zoom on that section of the screen you will see more vehicles, but obviously you don't want to that while trying to focus on changing lanes.

One tap down on the gear stalk activates TACC. A second tap down will turn on lane assist, or as Tesla calls it, Autopilot.

You don't have direct access to your phones assistant from the cars controls. But at the same time, you don't necessarily need it, or at least I haven't. You can turn on message sync on your phone and the car will display new messages you receive and you can then use the cars own voice assistant to reply. You can also initiate a new message from the cars voice assistant. For whatever reason, Tesla has decided that the Model 3 & Y can only answer calls by the touch screen - only the S & X can answer calls with the scroll wheels on the wheel.

The only time I use my key car is to give it to someone else who is driving my car. I only use my phone key as it's completey touchless that way (but you should keep a key card on you incase something happens to your phone).