Hi and welcome
You sound very much like my partner Z, although he had a SO when we met. It was an intimate but non-sexual relationship.
Two things to consider:-
1. Triads are tricky, very tricky, just been through one. Three weeks from go to wow and will not be repeating the experience.
2. While your wife might be "open" to your poly desires actually living through it all is a whole other deal. I was "open" as well but you don't know how it will affect someone until it happens. I would prepare her in advance by encouraging her to do some reading. This is a good place and there is also my blog (link below). If she doesn't show much interest (understandable), it would be wise for you to research on her behalf so you are prepared for things like jealousy which invariable comes up.
Good luck and again welcome