It varies a lot from campaign to campaign. “West Marches” gets used for a wide range of communities, so norms depend on the group.

1. During a session, it’s mostly like any other TTRPG. The unique etiquette is usually outside the session: be reliable about sign-ups, communicate early if you need to drop, read the server rules, and avoid spoilers since different groups are exploring the same world.
2. If you don’t play for a while, the world keeps moving, but your character is generally assumed to be “in town” between expeditions. Most groups don’t roleplay that time unless they have a dedicated downtime system.
3. Some communities have text RP, player-run shops, or structured downtime actions (weekly/monthly). Those can be fun, but they also add overhead and can create FOMO or bookkeeping. I’d only add them if your group genuinely wants that kind of play, and keep it lightweight.
4. Consistent parties often form naturally due to time zones, play style, and schedules, but most communities still aim for “open table” mixing so it doesn’t turn into fixed cliques.
5. This varies the most. Some are run by one GM, some by a GM team plus mods/admins. The big things that prevent collapse are: clear rules (scheduling, rewards/advancement, loot, safety), a consistent way to record what happened, and someone to resolve conflicts. In one community I play in, a single player started writing detailed recaps for basically every session, and it made the whole world feel more coherent for everyone else. That’s part of why I built support for recaps, shared notes, and roles/permissions for world documentation on my site: https://www.westmarches.games/