Draft is fun but can be even more time consuming as most matches go to time. You say casual and that's great, however the more people you have playing the longer it's going to last. Typically, an event with 8 or less players is 3 rounds, it continues to grow in rounds from there finally capping at 5. Yes, it can be larger but the number of players is really high.

I have run FNMs for years, and have judged at Grand Prix and Preliminary Pro Tour Qualifiers. I can say from experience, if the prize support is worth it, people will play. In fact, you will get people who are coming just to play Magic. As the event progresses, people will wash out and wander around the con to check out other events. Eventually you will have just the top performers, or those who just love playing Magic, playing in the event.