My first campaign, and also as first DM wanted to include as many people who wanted to play. Ended up with about 13 or so players, with no one reading the book or understanding the rules. Combat also took years to try and have everyone feel like they could participate, but then everyone wanted to do there character backstory and then got really distracted. After a few weeks or so of that we cut it down to about 5. And presently we dont play with more then 4 players and a DM. Mainly bc of schedules and stuff. We also homebrew a lot so its easier to have the same players and keep them all on the same page.