What is the difference between He would be... and he could be. Does it translate both ways in Polish?
mężem, to be exact ;) But yes, mógłby denotes a possibility (however strong it is), and byłby denotes being quite sure about that.
And I believe a direct English equivalent is "He's a good husband material" :)
Męża materiał, it means in Polish as husband's stuff/fabric. In this case should be - materiał na męża.