As I said in my comment on the major arcana, I'm interested in Tarot but not a fanartist - so feel free to kick me out if you don't want mere observers to comment.
Anyhow, I've had some thoughts on allocating the suits, which I thought I'd share here in the hope that they might provide useful seeds for discussion.
I've always used earth=coins, air=swords, fire=wands/staffs and water=cups/cauldrons. If you were going with JKR's allocations of the houses to elements that would make it:
earth=Hufflepuff... =Galleons, say? (Kind of works with the association of Nifflers and earth and gold, though I always figured people like the Malfoys to be associated with material status and wealth. Hufflepuffs are very earthy, though, and this association brings out the stability/hominess aspect to the element more than is usually the case).
air=Ravenclaw Perhaps quills would therefore be more appropriate than swords - bringing out air's emphasis on communication and discernment of truth more literally than does the sword?
fire=Gryffindor Which fits with the whole Phoenix thing. Wands fits as Gryffindor is our viewpoint onto the magical world, and broomsticks/staffs likewise with the amount of attention to Quidditch in the books. Alternatively, it would be possible to associate this with swords (I think I've seen fire associated with swords by some?) with the Godric connection, though it might be confusing if most people are used to swords=air.
water=Slytherin This is the one I have most problems with - Slytherin characteristics do not seem watery to me, but Jo Hath Spoken. I guess there is a Slytherin-potions-cauldrons connection though.
I realise though that this doesn't match the house artifacts (Hufflepuff cup, Gryffindor sword, Slytherin ring/locket and Ravenclaw whatever). I do think a consistent framework is necessary in order to use the cards, though (at least, I find it so), and using the house characteristics would provide one. I'm not sure whether that would make it necessary to feature characters only in the correct elements for their houses? It would be restrictive, but restriction is often helpful to give a starting point (the four founders would then be a logical choice for the Ace cards, for example). And it would be confusing (for me, at least) to use the cards if the associations were mixed.