I set the SSID for the 5Ghz different from 2.4Ghz.

5Ghz tends to work best in the same room as the Access Point, and 'the next room', not so well farther away with multiple walls in the signal path. So I configure the nearby and non-moving WiFi devices to the 5Ghz SSID. Apple TV, audio streaming box, that sort of thing.

This leaves the 2.4Ghz band and SSID available for the more mobile devices, and since 2.4Ghz penetrates structure more deeply than 5Ghz, the mobile devices get good signal everywhere.

Agree with running CAT6 cables to the equipment closet locations. Run more than one to each location. Cables do go bad sometimes, sometimes well after installation.

Also run cables to places where you expect connected gear to stay, such as TV, office desks, etc. I try to use wired connections whenever possible, thereby leaving maximum bandwidth available for the devices that must use WiFi.

A good wired connection provides the best reliability. WiFi can be quite good, but sometimes the solid connection using wired Ethernet is worth the hassle of installing it.