You’re asking the right questions!
I can’t answer these questions myself, because I’m just one guy and even though I’m a stream co-founder, my suggestions lack authority until ratified by a higher power: Be that a Constitutional Convention, ad hoc direct vote, decision of an elected President in conjunction with an elected Congress, or otherwise.
That’s what makes this stream democratic and what ensures it will stay democratic and responsive to the needs of the people, which is the only way to ensure its long-term stability and success.
Really, the only thing about this stream set in stone at this point are the anti-bigotry provisions. Those ideas are baked into the DNA of this stream and supersede even the Constitution or lack thereof, as it is what brought most of us here in the first place with the idea of building a better roleplay government.
Circling back to your question about the Constitution though, I would suggest we have at least a Bill of Rights, a formal procedure for elections, branches of government with defined roles, and impeachment provisions.
Who would write it? Either myself or we could break out different provisions to be written by different drafters. I’d prefer the latter so that I get a break and others get writing experience.