Always a pair of Ethernet, never one. Every other wall in most rooms and all walls in some rooms. Can be used for IR and speakers.

Just a BS browser notification, gotta go in your browsers’ settings and remove or block any shady sites you’ve given permission to show notifications

the dress is blue!

Don’t daisy chain them. One line from the main switch (your router) to each additional switch. If your devices support it and you can figure out how to setup LAG (link aggregation) you can combine two links to each switch for more speed but you probably don’t need that.