1) Asrock H81M is a miniATX board, and has only two PCIe slots, so no, that is not the board that you are using. What you have could be the Asrock H81 ProBTC or Asrock H81 ProBTC V2
2) Those arent 5V plugs, they are molex power plugs which can draw upto 12V. And you should not have them plugged in when using RX 470/480 cards.
3) Again, go through the forum threads, every answer you need already exists there. Please have the patience to read through hundreds of pages and try 10's of settings, we all did it.