I've always seen the wreath as Saturn because of it's relation to the laurel wreath that goes around the World card. The world card is part of a kind of "death" as in...this is the final end to your journey and you get to start over again soon. So that could be one of the reasons why there is a skull in that cup. Laurel has several meanings (the plant), one is victory because the ancient Greeks would crown the person with victory leaves, but the other meaning is prophesy, which is why (i think) it is used so heavily in Tarot.
If you decide to go with the 7 original planets then the Moon is associated with the HP and the veiled woman, so it couldn't be the chariot because the chariot also rules the moon.
I like the idea of the 7 deadly sins though because the 7 of Cups tends more towards being slightly negative because we get so caught up with all the choices and desires.
Lust: veiled woman
Greed: Jeweled Cup
Gluttony: Castle
Sloth/Sadness: Woman with the closed eyes who is all "blue"
Wrath: Dragon
Envy:Snake
Pride: Wreath
Of course, I'm going to have to think about this some more as I just came up with that right now. What do you think of the list?
I went to wikipedia
https://en.wikipedia.org/wiki/Seven_deadly_sins
One artist put Pride down as the tower of babel, so that might even be the castle.