Could start here.
My ultimate goal here would be to end up with two equal wives, all of us living in one house.
Could ask yourself what a "harmonious polyship for the next year" could be.
Could ask them what THEIR goals or idea of a "harmonious polyship" could be.
Because you are not a solo player who gets to pick for all. Do you all even want the same open relationship model?
Could stop to check in on that when you meet.
Maybe you want a polyfidelitious 3 people only circle. Maybe "open" to them
means something else. Calibrate your vocab and get on the same page.
You have that as an ultimate goal... but could also ask THEM what THEIR ultimate goals are. Maybe the goals all match -- maybe not so much. Not the time to hold back -- spill it all on the table and see what you all have there. What lines up and what does not.
Pitfalls? Try here:
The biggest pitfall to me is thinking this is already
the polyship. It isn't. This is "My wife and cheating affair partner are willing to entertain ending the "2 person marriage" and ending the "2 person cheating affair" and talk about creating a new relationship called a "3 people polyship instead."
This is just you all figuring out the details of the new offer on the table. Nobody's signed up
for it just yet.
You may come to find in negotiation that "nope... nobody can agree on the mission or shape of the potential 3 people polyship. We cannot agree on how we want to be together and how to handle conflict resolution or meet everyone's needs in a way all can feel mostly happy."
So then the conversation has to change topic. "3 people thing NOT gonna fly. NOT compatible players. NOW what?"
You may find you need to meet several times to cover all that ground. Could take the time to do it well -- since you have to mend trust and start building a new trust.
I hope for your sake it works out. But even if it doesn't -- could thank them for being willing to entertain it to begin with. Not many people get that chance after an affair.