This situation of yours has a number of red flags for me. Granted, I have just been dumped by someone after three years of being a secondary and I have little to say that would be positive. I will likely never put myself in a position again where my metamour is unexperienced with poly. I will not be someone else's guinea pig again.
Hierarchies suck and if this woman is saying that he comes first, is going to control everything, and that she feels guilty, I hate to be the one to tell you, but it likely won't work out and you will end up in a world of hurt. Sorry, not fun to hear, but its what so many experience and why sugar coat it. Of course it could be fantastic, and then you can make me eat my words... I love when that happens.
Having said all that, what I would do in your situation (I realize that love conquers all most of the time and that it makes us blind... I am have been blind also), is back right up and take it really slowly. I would let her know that I would be coming to visit her, get to know my metamour, talk with him and seeing how he does with a bit more time and getting to know me. If he decides that he doesn't like me and would rather veto me than see me be in his life as his wifes lover, then I would walk. To me metamour relationships make or break partnerships.
If I can't be an equal in her eyes and his after that, then I just wouldn't do it. I'm not saying spending the same amount of time, buying houses together, having kids together etc. which is what I see a primary partner as, I'm taking consideration and caring in the relationship. I would need respect in terms of negotiating boundaries and communicating needs. If I am not treated like I am just as valuable as he is, in my own unique way, then I would be walking. I am worth more than that. They would need to be autonomous from one another and be see each other as separate people, rather than a couple where one person has a girlfriend. Its just too depleting to my feelings of self worth and value and I just wouldn't do it.
There are many threads on here on secondary issues. I suggest you do a tag search for "secondaries" "secondary" "secondary rights" and read up on "vetos" "veto" "ultimatums" "ultimatum" or anything else that looks like it might help. The more you educate yourself about what could happen the better prepared you will be. You could also read my blog from mid Jan 2012 on and see what I have been through. Also several of the other blogs that are in the lifestyle and blogs section.... really, just stay here and read everything.... this is far too big and popular topic to focus on one particular thread.