Running a game with four to six players is ideal. This is because it allows the party to touch on all the major archetypes of characters: melee combatant, ranged combatant, arcane caster, divine caster, and support characters. Having a base group of four to six players means that if one or two people can’t make it to a weekly game, the rest of the group can carry on in their absence without feeling too short handed.
It is possible to run a game with more than six players, though having all of them in a game at the same time might be too much to keep track of, space might be an issue, and the time between turns in combat may cause some less devoted players to lose interest. If your group becomes too large, consider splitting it into two groups, or alternating players in different sessions.
A popular style of game includes a group-designed world, where a common setting is used, and each player is given the chance to run a game for a select group of players.
It can take Matt Mercer-like skills to DM for a large group effectively.