There are some current posts on building a quick mobile DJ ready that I’d suggest you read. They focus on buying some used (dance) samplers from various era’s. Same goes for Xmas music. I have a sampler with 5CDs (bout 110 tracks) of the most popular Xmas tracks ever. If it ain’t on there, I don’t want to play it. Ripping the Xmas CD’s and prepping the tracks would take me about an hour, tagged and analyzed and ready to go.
Getting 40-track double-CD good “decade” samplers for the 50s, 60s, 70s, 80s, 90s and 00s and the current pop/chart hits that are danceable should get you started imho.
Don’t be mistaken though. One of the traps I have seen club and genre DJs step into before is the sheer underestimating of the necessary skills for mobile DJ-ing. Mobile DJ-ing is not at the bottom of any DJ-ing ladder, but rather a DJ-ing ladder of it’s own. What we consider to be the #1 skill that makes a good DJ “knowing what must come next” is perhaps even more true in mobile DJ-ing, with a much larger palet to choose from.
Another thing to keep in mind that when you play clubs, festivals or other venues, people come for the purpose of dancing. Nobody comes to a wedding for the (sole) purpose of dancing. So getting a floor filled and keeping it filled needs a bit more doing. Not to mention having so many different tastes to cater to and to satisfy.
Good luck with your gigs, it will be a trip!
Almost forgot, the DDJT Wedding DJ course is definitely worth it’s money for your preparation and the playlists they contain.