I think the more imperfect the flow is, the more the different styles of the names will be highlighted. Almost all of the girls combos you came up with either have a double -a ending, share an initial somewhere or share a lot of sounds - or a combination of those.
Now, I don’t think flow is important but I do think it can act as a coherency creator.
E.g. [name_f]Freya[/name_f] Vellamo [name_f]Mabel[/name_f] rolls off the tongue, the names become one unit, one name. [name_f]Freya[/name_f] [name_u]Florence[/name_u] Onerva shares the F initial and the double -a ending, which creates a choppier flow and you pay more attention to the individual names.
So, while I personally don’t think it’s important that a name flows well, creating a combo that does flow well will make almost any names sound coherent together.