Re: First Wife's Permission
From what I could gather, if a woman wants to restrict her husband from plural marriages, then she should put it down on the nikkah paper/form. If the husband breaches it, then she has the right to ask for a divorse.
If such a term has not been stipulated at the time of nikkah (or on nikkah form), then the husband could get married again without requiring his wife's permission.
Yes, it is a bit shady. Hopefully if I get a chance, I'll try to get some clarification for myself, as this could be helpful in future.