Welcome Reuben! So good to have you here! Since we know that having a second wife, is not sinful, and we know that God is the One who gives us men the desire to marry, you can be assured that this compulsion you feel to have a second wife, is from God. How to get there, however, is dicey, as you, like the vast majority of us, probably live in a monogamous culture, and your wife married you under the presumption of monogamy. She will be devastated when she finds out that you desire to take a second wife. There is no way around that. She will feel like the marriage is over and that you no longer love her. She will want to know why you need another wife. She will want you to go to counseling. She will see this for the abnormality that it is, unless you live near Hillsdale or parts of northern Mexico, and that is a very unsafe feeling for her.
I would suggest you ground yourself in the Biblical arguments for polygamy, and familiarize yourself with how to defend against the arguments others employ in their efforts to deem polygamy to be sinful, first and foremost. If your wife thinks that this desire of yours is sinful and from the devil, she will have no trouble finding people who will tell her that she should walk away from you. They will have her convinced that you are an apostate, and that is enough rationale for a lot of people to do so. I am not saying that they are right, because when I read my Bible, I see nothing that would rationalize this idea that if your spouse apostatizes, you are free to divorce them and remarry. However, you want to be able to point out clearly and concisely what the Bible says, because you also want to have the respect of your wife, as a Biblical leader in your home.
This site here is the perfect site for you to learn how to bolster your arguments. We have a thread on Logical Fallacies that Anti-Polys Love to Employ, and how to identify them. We have Biblical references that you can look up, to prove some of the arguments that we put forward, and those are critical, because some anti-polys are familiar with some of our arguments, and they will employ all kinds of responses, in an effort to dismiss our arguments. I would encourage you to go online to various forums and present the arguments that you are familiar with, in order to prepare you for the onslaught that you are going to face in the real world. Try to use the strongest arguments in your arsenal, and avoid the weaker arguments, because you will want to be able to able to hold your ground, and you don't want to use an argument that you will have to concede on. Be aware that you will take all kinds of guff from people, who will impugn your motives, and are convinced that you are on your way to hell.
Refer back over here to this site, whenever you get stuck on an issue, because we are here to help, and you can search this forum to find many of the answers you need. Also, Brian Kelson and William Luck have excellent videos that I would encourage you to watch on YouTube, to deal with the toughest challenges you will face. I encourage you to watch Luck's video on Lev 18:18. This Angelo Tosato fellow, that the anti-polys are relying on, was a Roman Catholic priest, and his claim, that the Qumran community, which was in fact anti-poly, interpreted "sisters" broadly, is patently false. After you have had a few months of online debate, where you feel you have either convincingly won the argument, or your opponents have to resort to extra-Biblical writings, and so-called "experts" like Tosato, and you can claim the Biblical high ground, then you can address this when you have to face the minister, which you will inevitably have to do.
You can expect that your efforts to persuade the church leadership, will be rebuffed, but it is not futile, as you will probably have your wife with you, when you interact with them, and she can see for herself how you are able to refute the lies, and quote Scriptures that the men in your church's ministerial staff, have never read. Another thing you will be able to do, is you will be able to sit down and have lunch or dinner with your fellow church-goers, and present the arguments that you have familiarized yourself with. I would strongly encourage you to do so with as many men in your church as you have opportunity to do so, because when your church enacts "discipline" on you, which is inevitable, you can have plenty in the church, who will have your back. The church may think that the leadership has the final say so, but the reality is, that the leadership is nothing without its membership. You should strive to be the most engaging and friendly person in your church, so that when the church removes you from whatever leadership position you may hold, it won't set well with the membership, and especially with those whom you have had an opportunity to persuade. You won't reach everybody, but be willing to agree to disagree, as long as they understand that removing you from their fellowship and leadership positions, is not exactly agreeing to disagree. You are going to have to have some thick skin, but you get used to it over time. I have learned to tell folks that I won't stand before them on Judgment Day, and their opinion of me or what I stand for, doesn't really matter.
Learn who in the Biblical Families community, lives near you, or somewhere in the vicinity where you reside. When you and your wife are able to develop a close friendship with like-minded people, it will make the likelihood of getting her on board, much greater. Hold fast to her patiently, because if God is in this, He will work things out. You are in for the ride of your life, and I am saying this, without having gone to the next step, by having a second wife. The only experience I can speak from personally, is getting my wife to accept polygamy. Those who have a second wife, will tell you that you are in for an even bumpier ride, once you reach that step. Hold on tight, and enjoy the ride! We look forward to hearing feedback from you on how things are progressing.