Gotta put in my 2 cents if I may, SirDJ:
While all of the above suggestions are good, it might be a good idea to spend a bit less in the beginning for more titles. Once you get an idea of what's popular in your venues you can always buy the above.
IMHO, the very first set you should by is SuperCore. This is actually a split set. I believe the original set is 38 discs, ( SPC01 - SPC-38) Plus an update set ( SPC-110 and up) of approximately 15 or 20 discs. These are good quality tracks, and the selection is some of everything. The whole set can probably be had for under $300.
I would also get- believe it or not- the 66 disc Sweet Georgia Brown set, if you still can, LEGALLY! Though not well known for high quality ( some tracks are actually great, but they have plenty of misses), they have a great selection of things like jazz, metal, and eclectic song you may not find elswhere. For under $100 for the set, you really can't go wrong.
This low cost will give you around 1800 songs ( unfortunately, there will be plenty of dupes in the Supercore set) of all different styles. Once you have an idea of what your venue/area prefers you can step up a bit. If it's country, for instance, Pick up one of the Chartbuster sets..... Top Hits/Pop Hits monthly subscriptions can keep you up to date, though I don't use them anymore.
One other personal opinion: Unlike many karaoke hosts, I DO NOT eleiminate duplicate title from my books. You will find that many of your singers prefer certain versions of a song. If you have White Rabbit on Sound Choice, SuperCore, and All Hits, keep all three in your book. In this particular case, though I have about 5 versions, and Sound Choice is a very popular mfr., The All Hits version is by far the most popular. I wouldn't have known that, and kept my customers happy, if I didn't have it.
OK, one one other thing. Though you will be PC based, it's a good idea to have a player ( with built in keychange if your PC can't interface) set up as well. Many singers carry the discs that they practice with. Some hosts may not, but I've found it to be a hell of a selling point when you are trying to build a following....
Guess I'm on a roll: Make sure that you understand that, unlike DJing, the vocals (midrange) are the priority when mixing sound. Going along with that, quality mics are a must, as well as speakers with a good midrange response........ Geez, I talk to much :sqerr: Good luck and keep posting!