I am a KJ only, and I am considering getting into DJ work to compliment the Karaoke.
For the basic stuff I do, DJ Mix Pro is fine. If you are looking for something that is infinitely variable and can mix, beatlock, beat adjust, and cross fade on the fly, FOR FREE, you might want to look into ZULU DJ SOFTWARE.
http://www.nch.com.au/dj/index.html
It rocks! It is much more capable than DJ Mix Pro, but it is also a little more complicated, and it will take me a while to figure everything out. It might not be so much of a learning curve for you. It is very polished and works great!
Good luck, let me know what you think of Zulu.