Again, go through the setup and come back to me on that.

One thing that jumps out is that a lot of shared narrative stuff gets established in that very first session. I think a rotating cast would be most successful if somehow everyone who will participate was there at the beginning for a “session 0” setup turn. Then, yeah, mmmaybe folks could come and go. I’m not at all persuaded it’d provide an optimal experience though — but if accommodating a varying group is the most important thing, then suboptimal isn’t so bad.