If you're looking for potential pitfalls I'm gonna tell you right away don't ever say that one fills holes the other doesn't ever again.
Ok that could just be my opinion but as someone coming from a somewhat similar story I winced.
Maybe that is true for you and maybe these two woman could handle knowing that. Personally I look at my two relationships as two people I would want to be with if the other didn't exist. I imagine it would not feel great after 25 years of marriage to be told, hey you actually weren't filling all my holes all these years and now this other person does but don't worry you fill holes she doesn't too YAY! I can't tell you how much time I have spent trying to make sure my husband knows the reason I have another relationship is NOT because he wasn't enough. I guess for me that is true. Maybe I'm overreacting.
Next slow way way down. You might be imagining all of you living together in that equal harmonious home but they have never met. That fantasy is a long way off IF it ever happens. Tell yourself this now and you'll save yourself a lot of frustration and many many mistakes pushing for something none of you are ready for. Manage all of your expectations. Unless your wife has been sitting around secretly wishing for this to come along and U just happens to end up being the best friend she's ever met or something, it seems pretty unlikely she is going to see this as the best thing you've ever done together. Even if she does, it won't be 6 months from now. Read around a bit in the blogs section. Relationships like this have growing pains. It's a whole new ballgame. Your ultimate measures of success just sound way too high right now. I'd be looking for things like no one cried today, it was a good day.
I get it, you are probably elated this possibility is even on the table. For me this is the happiest I've ever been and at times the worst pain I've ever felt. It is far from all heaven all the time. Thats the advice the struck me immediately, slow down, manage your expectations.