I ran a tournament at my house in the fall with 20 people and 6 games. I tried to imitate PAPA's Pinburgh model as much as possible, which gives everyone the opportunity to play as much as possible and also re-seeds everyone after each round so you're constantly playing people close to your level.
As a "qualifying" phase to get into the finals we played 6 rounds of match play using the "Monthly Master Tournament Software" on an iPad which separates all the players into 4 or 3 player groups, and then after the round is over you can input who got 1st, 2nd, 3rd, and 4th, which gives those players 5pts, 3pts, 3pts, or 1pt respectively. When you generate the next round the software automatically creates new groups based on the results of the previous round(s).
After 6 rounds, "qualifying" was done, the top 12 formed the "A" division, and the bottom 8 formed the "B" division. The "finals" phase would begin now where 4 players groups would be formed again based on your qualifying seed, and this time you would play two games with those groups using the same scoring system (5,3,2,1), the two players with the most points after two games would move on.
The "A" division would do this 3 times, with seeds 1-4 getting a bye for the first round joining the remaining 4 players in the second round.
"B" division would just do this twice with only 8 people to start.
I know that sounds like a lot, but its not that complicated and was a lot of fun, keeping everyone in it for as long as possible while making each phase of the tournament important. Again, it was really just a hybrid of PAPA's World Championship and Pinburgh models but for 20 people.