Yes - that's how you set it up. One wired powerline plug connects to your router and one (or more) wireless powerline plug sets up its own WiFi zone. I live in a large stone building and the router's own WiFi signal does not travel very far at all.
Yes! I did the same bought a pair of TP Link and then bought the wireless 6 months on. Just remember to pair with the pair button. I think I only did this on the one unit. I have not had a problem when using.