If you're just getting started with print-and-play card games, here are some tips to help you.
If you are printing them out, you can fit 9 cards in portrait orientation on a single piece of paper, arranged in a 3x3 grid.
The quickest and cheapest way to get started is to print the cards on regular floppy printing paper. Cut the cards out, and sleeve them in opaque sleeves, using old or unused cards (like Magic: the Gathering or Pokemon commons) as a backing.
The nicest option is to pay a professional service to print them for you. The official Keyforge Adventures have been set up at online printing services.