I'm interested in installing OS 10.8 Mt. Lion on an external HDD, which would be used as a dedicated drive for working on video/audio/graphic files. Since I'd like to preserve as much disk space as possible, I'd like to know what the MINIMUM OS installation would be for doing this. By minimum I mean only those core OS 10.8 files that would likely be necessary for booting the drive and operating additional installed video/audio/graphic software. Any insight that could be passed along would be most appreciated.