one way to avoid losing any movie info (forcing you to rescrape everything which will take a lot of time), is to use an external scraper and construct nfo files for all the movies folder.
this way the movie info and images will be stored directly inside the folder rather than inside the database. so avoid any problem with xbmc migration. it'll also be much faster scraping time if should there's more than one media player accessing the library.

xbmc on an external drive, or running on a media player will be too slow if there's more than a couple of drives connected.

sorry for the late reply.
just install the program, point the settings to the media folder and you can start scraping. oversimplification, but it's as easy as that.
tho make sure to put each movie into separate folders. the scraper will construct all the necessary info file and images inside the folder.