Just like Chris k said, never use smart connect.
And no, you can't make a login for only the 2x 5ghz. Here we use 1 5ghz on the first and the second on the second floor 🙂
The AX11000 has a lot of options. What I like are those AIProtection options. Ye, it will cost you some privacy but it will make things more save.
Also the Traffic Analyzer works very nice. Just turn it on and wait a couple of days.
I also use the USB connection with my external SSD to have a media server. I even use the FTP funtion as backup for my security camera's.