Kodi (XBMC's new name) will do all of what you want for you.
Install Kodi
Go into the 'Videos' section, Files, Add Library.
Select your media share
ie..
\\nas\movies
Tell it what source type it is (select Movies), go to the Settings option in that screen, change it to IMDB ratings.
Hit Ok/Next and it will scan the video filenames and download all the artwork, movie info, imdb rating and build a Movies menu for you on the main screen.
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Now go into 'Movies' and it will have all your films listed there with a nice GUI. You can press Left, or Up, Left to tweak the GUI.
I'd get comfortable with the default skin before adding any addons or making any changes. Better to know the program inside out before fiddling imo..
Is your NAS a Synology?