I'm going to touch on a few things here.
debcub wrote:What would be wrong if my wife could use Debian without waiting for me to come back home and do "# apt upgrade"?
Nothing, if you trust your wife and you are a root user you could give her the ability to run the apt update and apt upgrade commands. You just don't know how to do that. You'd have to learn how to give rights to run those packages in sudoers. But it won't be a GUI that you as root can just click.
I'm still using Jessie so I can't check Stretch for you but I think it likely that the default configuration for unattended upgrades would be just for security upgrades. So when you found 200MB of upgrades available after pressing whatever button you pushed, were any of them security upgrades?
In my second post in this thread I gave you a link to the Debian Wiki.
Have you confirmed that things are configured the way you want them as per the info in there?
Personally, I don't think I would want my system to automagically upgrade, that takes some control away from the system administrator but it could be your choice.
Except perhaps in the case of a server that runs 24/7 and you don't have 24/7 administrators.
The simplest thing would be for you to return to Ubuntu where those things are done for you.
Good luck!