Hi Wicked. I missed your post back in Jan as I was off the site. I hope a delayed response is still of some use to you.
1) Since I am not female, I cannot give you anything other than my perspective. I would gather that nobody wants to be last in line. What is usually true is that a new wife lacks history with the family, so if there is conflict (as there certainly will be at some point) the fear is that more established members of the family may band against a new person. But that lack of history can be a doubled edged sword. I am more likely to pause a moment of irritation if it is the first time something has happened to me, instead of the 12th. Meaning, even mis-steps in family life, finances, child rearing, etc can be easier to forgive in the heat of the moment with a newer person. Ideally a first wife has more political equity and sway, but in reality we all have different things that we do well for the family, so it works out a little more organically. I think the regimentation of hierarchy only exists in either deeply religious families or cable TV shows.
2) Again, not a wife, but I expect if we had a more significant imbalance (4 or 5 wives) then adding another person would water down personal time even further. I think each person views this differently, and at different times in the relationship.
3) Yes, in the scope of underlying reasons and trying to talk things out to avoid conflict or bad feelings. No, in the sense of the placement and title has pretty much zero bearing on how our family operates in day to day life with the rare exception of introducing Heidi as my first wife and Molly as my second. Individually they usually introduce the other two of us as their husband and wife.
I hope this provides some perspective.