All cards are practically the same, except the copy on them and a few images specific to the card.
You need a card.
You need the info to populate the card and load in some custom image (character portrait).
And you want user to customize it....
Text file or json (both are easier than xml)
Text use tokenat or regex
json load into array or dictionary
I know c2 can load images in, they just need a url which can be stored with all the data in text or json.
Not sure if you can include from folder, but you can have user pass a url via his text/json file.
Edit: I am talking from not actually having done this to such a degree