Any numerological system is essentially arbitrary. I'm making one up, and I hope it'll be internally consistent. This is how I plan to assign divinatory meanings to the cards, in the hope of someday making my own deck. The general idea is that you combine the suit significance with the numerological significance in order to obtain a more specific meaning. If you are using a pictorial deck, you should also combine this with the impressions left by the card itself. If you look at the various schools of thought on divinatory meanings of cards, it is evident that many of those people used this same method. Please note that this is a work in progress, so your comments are triply appreciated!
Newly updated with additional numerological suggestions as of 5/22/13!