I think you might be getting a few things mixed up here.
The Dominic system is intended for turning numbers into memorable images, by turning each number into a letter-based abbreviation. Like 80 becoming “HO”, which could become the image of Santa Claus for example.
See also our wiki page:
Sidenote:
You might end up with numbers that are harder to imagine, that is natural. Practice makes perfect here, and even if an association starts off weak, it will become stronger with practice.
Now, moving on to the cards. What you have is perfectly valid, I use a similar system for cards and I have even used this to create my millennium PAO. I call it a category system, but some different names have been used as well.
It seems you have your categories down pretty well, so next would be to assign the cards. What I recommend is to make some associations.
6 of hearts could be the Hulk for example, as the 6 could look like an arm with a fist.
King of diamonds could be Donald Trump, for being a pretty interesting POTUS.
7 of clubs could be Christiano Ronaldo, for famously playing the backnumber 7
You get the idea 
Perhaps you might also be interested in our getting started guide, for some useful tips and tricks: