Keep it simple

Jus one tine

If your house was built before 2003, that's probably the case. Otherwise it MAY have cat5e cables in it that were used for landlines

I just have cables outside of walls, along the corners. And doors have enough gaps usually at the bottom to let a single Ethernet cable through and still close without any problems. It isn't very noticeable even without drilling.

On Android it likely will, I have done exactly that before. Kinda looks weird to see a ethernet symbol where the WiFi icon usually is

I've done that a few times to reverse tether Android phones and tablets