My husband wants a co-wife. Is it correct for me to meet her and try to find out if she will be a good fit for him and maybe a friend to me and be able to honour him like he deserves ? My husband is ok with it, but am I stepping into something that does not concern me, as it is their marriage ?

May Allah subhanahu wa ta'ala reward you for taking this with such ease of heart and thinking like a mature woman. That quality is almost extinct at this day and age, except for those upon whom Allah subhanahu wa ta'ala has bestowed His mercy, like you. You are thinking very positively: that you can be friends, you can be sisters, and you can have somebody in your life who is an aid for you rather than an enemy, which is how it automatically becomes with the vast overwhelming majority of women today. However, that being said: 1. If this is going to cause problems, I really do not recommend it. You can let them be as they are, and it would not be your business. 2. If that is not the case, and genuinely both of you (Allahumma barik) are mature women with nothing in your hearts—and you really think you would like to have a friend and she is a fit and feels the same way—then there is no problem in that at all. Assess the situation and do what you think is wise.