What should I consider before posting a card that can use multiple kinds of quanta?
1) You should consider what type of "multiple kinds of quanta" you are referring to. (Though I have a guess)
Duo
Duo cards use one type for a casting cost and one type for the activation cost. Note that a duo has an activation cost matching the theme of the activated ability and a casting cost matching the theme of everything else including passive abilities.
Other
Other cards use any type of quanta for their costs. As such they are meant to be able to fit in the theme of any element or be generic enough (like Longsword) not to need any element at all.
Hybrid (my guess)
Hybrid quanta is a pseudoquanta that can be paid with any combination of two types of quanta including being paid in full with only one type of quanta. At the core Hybrid cards are 2 mono cards with identical mechanics. A hybrid Air/Aether card would need to make sense as a mono Air and as a mono Aether card. Unlike duo, only themes native to both elements should be used on a hybrid card. Air controls storms which involve Lightning. Aether controls electricity which involves Lightning. Lightning can be used for a hybrid card because Lightning is part of both elements.
other forms of Pseudoquanta
Each pseudoquanta has its own kinds of thematic requirements that are derived from the pseudoquanta mechanic.
Essentially it boils down to this: Any effect that can be paid for with only
should fit Aether thematically.