Of course if you own your own home, you can put in all the ethernet you want.
In theory, yes. In reality it means knocking lots of holes in the walls, drilling through floors, etc, etc.. That gets expensive / time consuming. The previous owners of my house had the thing (built 1890) wired with coax and it all runs on the outside of the house. I settled for running one CAT6 cable from my office on the 2nd floor to the basement. Otherwise I'm stuck with WiFi.