I've been doing Karaoke on and off for the last 14 years or so.. generally when i'm in between bands.
I play two clubs regularly every week, and find that I could really do both shows with just a few hundred songs.. if you figure a 4 hour show, average song length 3 minutes, plus the time it takes to cue up the next singer.. you're only reasonably going to get 10 or fewer singers up per hour.. x 4 hour night, that's really less than 50 songs you'll play.
And that's if you have non stop singers.
I always end up singing a few myself, or playing DJ music during shows, especially at the beginning of the show to fill the gap between singers.
So i'll echo what's already been said in this thread: it really isn't the number of songs you have, it's the titles of the songs you have.
I like having a wide general selection just in case, especially when you go into a club for the first time and really don't know what people are going to want to sing. If someone requests something I don't have, I make an effort to get it and add it to the collection.
As to the top 100 most requested Karaoke tracks? Check out this list:http://www.validmusiccentral.com/Most%2 ... 0Songs.pdf
Of course the actual popular list in your area will vary slightly, but generally speaking, i'd say that list is pretty accurate.