Using the fantasy cards makes the game significantly easier. With TheBoss it only takes one or two Headshots with the basic Handgun to kill a zombie and they hardly deal any damage. The double ammo code should give you more than enough of that since you get a feeling for where ammo can be found in the game after a while. Post #2,422 and #2,423 have all essential codes (the active patreon code can be seen on the title screen).
I like the game so far and I'm looking forward to see the boss (hopefully some weird creature like in the RE games and not just a really big zombie inspired by Nemesis or Mr. X).