I would say for a small 8 player day tournament you set it up similar to how mafia games are set up. Create a thread with sign-up sheet and the rules. People can /in if they want. When it is full, start the matches.
With the rules just state how you plan on matchmaking and such. Mafia games have rules for posting frequency and such. You can make rules for how quickly the matches need to be played, what format the matches are going to be in, anything you want.
If people don't like the format, they don't play. If they do, then awesome! Also, people can start hosting day tournaments of various sizes and styles. Round robin, single elimination, double elimination.....there are options.
I mean, thinking about it in a mafia sense...we have drunk mafia, blitz, RMM, standard....all types as well as very large or very small games. Mods of the tournament can specify what type they want. Do they want serious, do they want a specific rating range, do they want all games to include scout? Doesn't matter. They created the mini-tournament and put it out for people to join.
And I think people will join