If you have to choose all the music then why hire a DJ? DJs play music at parties for a living. They're supposed to know what works and what doesn't and how to adjust according to the crowd. A good DJ knows what to play and when. Of course, it's necessary to specify some of the music your event will require like first dances and other "must-haves." But if a DJ requires you to submit a list of all the music you want played, work with an online database to make your choices, or worse, demands total control as to what music gets played based on "expertise," consider another DJ.
With Chris at the helm of your party, you are free to specify as much (or as little) music as you like. The process starts with you reviewing a list he has prepared, and modified over time, of about 100 songs. It is based on years of experience as a DJ. You are free to check off your favorites, and scribble out the ones you don't like. Everyone's tastes are different, and no playlist guarantees success at every party. His list serves as a glimpse into his style as a disc jockey. No matter the crowd in front of him, these are the songs that have a proven track record for success. Once you've reviewed his list, marked it up, and sent it back to him, your choices serve as a window into your musical tastes, and as a starting point for further discussions about the music for your event.
Six hours of service is enough time to hear about 100 songs in their entirety (but when mixing at most events, songs don't play from start to finish so that number will be higher). A lot of times, half of that time is enjoyed during cocktails and dinner and the rest of the time you'll spend dancing. In addition to the list of music Chris supplies, you are free to offer your own ideas. Some of your songs will be used during cocktails, and others mixed into the dinner music. Naturally, many of your suggestions will be best used during the dancing.