Thanks for your thoughtful response, I really appreciate it.
I think we're working with different assumptions. You're assuming that all co-hosts want more involvement. I assume the opposite: most co-hosts only want to be involved when needed.
Regardless of our assumptions, I have found a co-host who will do it according to my assumptions. I only need assistance 2-3 times a year, while I'm on vacation: February, May, and sometime in the summer: a maximum total of 25 days a year. The rest of the year I can handle. This arrangement is precisely so that the person doesn't feel overwhelmed, having to do it on a regular basis. I've done it htis way previously, informally, and my aim now is to make it more "official" so that the co-host doesn't just have to rely on "my word" (ie - earnings) but on an open/transparent access of information. Everything is above-board.
Most bookings will have been made in advance so that it's more a matter of "seeing them through" than accepting new bookings. The co-host would primarily be responsible for welcoming new guests, answering inquiries, emergencies, and cleaning/laundry afterwards.
I would do calendar before I leave, and while I'm away it would be a joint effort.
Regarding reviews - good point, I hadn't thought about that factor. I would do them, relying on the co-host's feedback, although I wouldn't be averse to the co-host doing them.
I appreciate the feedback re: 25-30% pay scheme. I was astonished to find out that virtually no one else has posed the question of pay scheme, which is why I asked it. Again, very helpful, thank you.