Can I just say, from an outside perspective, a poly bi woman, just from what you posted here, this is what I see:
"We are a committed, long term couple looking for a woman that will be interested in dating both of us, romantically involved with the husband, perhaps the wife, be home for the wife when the husband is traveling, home with the husband when the wife is traveling, and add to our marriage."
My first reaction is, "Get a dog". Think about what the third person gets out of this arrangement. Also, being in love with hubby is not enough. You've thought about how warm and cozy she will fit into your life, but again, almost like you would a pet. What do you offer her? If the answer is only a stable home, a roof over her head, companionship, then it's not enough. Start substituting a puppy for the girl and if the only thing that is different is sex, you have much more to figure out and work on.
Me: Late 30s pansexual poly.
DH: My husband of 19 yrs and father of 3 teen girls.
DC: LDR of +4 year