First of all, are you infertile like me? If not, what is motivating you? If infertile, my recommendation is that you make sure you can handle the knowledge of who is fathering the ....... Obviously another man's seed is impregnating yoiur wife, but if you do it through medical means, you really never know who the guy is. If your wife takes another man's cock and he makes her pregnant, you will always know who he is and in the back of your mind, you will know he is the bio father.
If you really think you are okay with that knowledge, and your wife wants to do it this way, then it is important that you both agree on the guy. Secondly, unless for some reason you want this guy in your ......'s life, you need to find a guy willing to do it but who wants no parts of the results.
Make sure you get all medical information as possible.
As for the act, you need to decide if you want to witness it, if the guy is willing to let you watch, or if you just want the knowledge that this guy put the baby in her.
We did not take this decision lightly and we took our time, until we found the right guy. I was there to watch, it was sexually exciting to watch but also it was hard for me to know he was doing something i could not. But knowing how much my wife wanted a baby, and doing it naturally, I had to leave my jealousy and ego behind and just enjoy the moment.
If you need any more guidance, just let me know.