@reason I would never open a MUSH that is not substantially complete. By susbtantially complete, I mean:
- All necessary theme files are in place so that people coming to your MUSH understand the game and what it is about. This includes any files about different races, places, any magic systems, setting, etc.
- All policy files are in place, including your expectations for conduct of players and how to report other players
- The grid is complete and descriptions are done. This doesn't mean that the grid can't be expanded upon, but you should have the basic grid done with a dozen or more places for RP depending on your theme.
That doesn't mean that these things all have to be SET IN STONE and nothing can be changed/updated/etc. All games will need 'polishing' as you kick the tires and see what shakes loose. But putting up a game that doesn't look finished, or where you start crowd-sourcing for a large majority of things (room descs, abilities, monsters-of-the-week,etc.) just spells trouble and I have not seen a game gone up that's done that and lasted very long.
As far as critical mass of initial staffers - ehhh, that's gonna depend on so many variables that it's not worth it. @krmbm and I ran Gray Harbor on just the two of us, but we did eventually ask for help with applications, building and most importantly storytelling as the game got larger. It depends on your own personal ability to run the game. How much time can you invest, etc?
Critical mass of initial players, again that really depends and I wouldn't focus on that. You have to ask yourself what you consider successful as a game runner - that could be a population of 5 or 500, and it's not something you can necessarily control either.
Existing metaplot - ehhhhhhhhhhhhhhhhhhhhhhh. Metaplot is not something I'm necessarily strong with and it wasn't important to me. It's way more important that people have something to RP about and something to base their own stories off of. That should be in place as of Day 1.