I play quite a lot in a couple of related wedding/function bands, and agree that 200 to start is a hell of a thing to burden everyone with. We work from a songbook of about 100, and clients can pick from that, but we inevitably end up playing a core of the same 20 or so, with a selection from another 30, and the last fifty are firmly in the 'we can if specifically requested' camp, which can take a bit of brushing up on (although we don't go as far as to actually rehearse ).
Even given a 100 song list, virtually all clients are happy to go with the band's selection within an overall mood - after all, very few wedding DJs get given a full setlist already specified by the bride...
I'm not convinced the 'we know more songs than the others so we must be better' approach actually works, either.
In order to keep things positive, I'd suggest a band meet to discuss the 200 to 'prioritise' them - with luck, you'll find a lot will wither away due to lack of interest.
If he wants all 200 ready to go right away...he's delusional...back away slowly, and keep smiling...