Regarding Throwing Stars.

Damage range shows the first "attack"'s damage, which would use the 1 Ilbi. When you use L7, it needs 2 stars, so it goes for a pair of Icicles.

As far as I know, Soul Stars is the only skill that will take stars from multiple sets - but it will only take from the same kind. Eg. if your inventory is 1 ilbi (100 stars), 1 icicle (1000), 1 ilbi (1000), and you cast it, you end up with 1 ilbi (0) 1 icicle (1000) 1 ilbi (900). Then the next time you use it, icicles drops to 800. If you have <200 stars left of a given kind is the only time it'll skip a set.

Makes a lot of sense when you put it that way. The amount/type of stars are determined when the offensive ability is invoked, hence implementing the effects of the stars chosen for the ability. I get it, thanks Steoreo.