How to manage miniatures and fanart?

Hi there forum'ers! I have quite a trivial question. All my movies is stored on a server and I want to know what the most optimal way is to store miniatures and fanart? Each folder on the server that contains a movie, contains subtitles, .nfo-files and a miniature scaled down to halv of 720p to optimize the system. But is that the best way? I'm guessing maybe my ATV2 would run faster if I store all the miniatures locally instead of on the server? But let's say that storing miniatures on the server is fast enough, is there a way to make XBMC automatically use the .jpg in each movie-folder as it's default miniature? As it is today, I have to manually change the miniature for each added movie.

Thanks for your time.