To answer your original question, computer based systems will require about 6 gigabytes per 1000 tracks of ripped mp3 and the accompanying cdg or mcg files.
To play them there is a choice of several programs, these are some;
Winamp -free with a cdg plugin downloadable from the web, version 3 is a poor version with too much overhead, and version before that or the new version 5 is fine. (version 5 will work with the old cdg plugin)
Wincdg. this will play direct from cdg disks or process mp3 and cdg rips. Purchase from Tricerasoft. This will also rip you disks to mp3 and cdg files. NOTE these files are 3-4meg in size compared to 30-40 megs on the original disks.
CAVS PlayCDG, purchaseable from cavs will play disks or ripped files, the graphics files must be ripped to .mcg format, this is much smaller than the .cdg files, so you do not get as many software player options. CAVS also have a supercdg software player, autorecognised on all commercial SuperCDG's. so if you have a compatible drive it will play them.
Karaoke Builder Karaoke Player will play mp3 and dcg or from the disk.
If you go the play from disks path you will need a CDG or SuperCDG compatable CD or DVD drive in the computer. Plextor and Sony seem to be the most popular.
The graphics are displayed on the standard vga screen, so if you want to buy a video splitter you can run a monitor and a performance screen. I use lcd screens nice and light and high definition in any light.
If you go the laptop route try for one with a seperate vga out option to cut a few costs and allow a second performance screen. Some have video out as well.
Audio goes from the computer to the mixer.
Hope this helps