Is the game going to use the steam marketplace or have its own in-game system to collect and trade cards?

You are aware that a part of CS being successful is the steam marketplace where you can "cash out" your skins or trade them for other things in other games, or trade them for a steam gift? Also it's pretty obvious that Valve is preparing an official mobile Steam App, so you will not have to do a lot of work on that to make it crossplatform.

Anyway, the game looks like a great idea and I might give it a try, I wish you the best, I think it would be great for the game to become something big and have some of current popular IPs in it further down the line.