Regarding the idea of your own card, there could be like certain images you start out with, and the card gets stronger for everyone as you do... Example:
Bob has his own card, Bobbo. He's level 1. Jack has a copy of Bobbo the card. It's level one. But suddenly Bob levels up to lvl2! All Bobbo cards are now stronger, possibly a new image, and have a different attack, including Jack's copy
Sort of confusing but that'd keep it constantly growing in a way... and what kind of quests would there be to get stronger cards... you have to face others in a deck battle?