Can you share a bit more about the art generation? Are you using StyleGAN or some other architecture? Are you hand-selecting the art from among generated images? What training dataset did you use or create?
For training, I spent a lot of time scraping images. I couldn't find any good dataset for this purpose. Controlling for quality is pretty tough, and I didn't spend nearly as much time as I should. And it's evident in the result. Some of the generated arts have pretty low pixel quality if you look at the original image. Luckily, it looks ok on the cards.
"Leveling" and "skills" are game mechanics, true, but what are the rules? You must have something in mind. Right now I have no idea even if the intent is solo play, 2-player, or more. Much less whether it's cooperative or competitive, deck building or engine-building or just tactical, and so on. How about whether there are going to be other (possibly a non-collectible core set) card types?
This is a fun project I've been working on recently. The idea of the cards started when I saw how an AI could generate realistic portraits of people. I tried to apply similar techniques to generating fantasy characters, and got amazing results.
The next 2 weeks were spent on designing the card assets, hero traits and descriptions. I borrowed some ideas from D&D (attribute points and alignment). Also threw in a random name generator, of which the names were scraped all over the internet.
Once I had the card assets, the rest all fell in place. It was obvious that the Ethereum blockchain was the best market place for such a collectible game. I spent the next 2 weeks writing the smart contract (based on ERC 721) and various pieces to support trading on the site. Fun fact: ETH price took off right before I was ready to deploy the contract on the mainnet. Due to high gas price, I had to spent a fortune... not fun!
I had a lot of fun working on it. Let me know if you have any questions.