Like Xrystal said you might want to try disabling everything that isnt nUI and taking a look at the addon with nothing else on it. Then consider what you want to see in your UI. Right now you have an extra unit frames showing the information you already have in the center of your screen. When it comes to the mail if you want you can get a FUBAR or Titan panel addon that alerts you to when you have mail. Personally I disable the nUI use of the minimap with /nui minimap then use an older addon called Simple Minimap to have my map in the corner where the default minimap is.
This is an older screenshot but this is my what I have my layout like:
