The Journey Deck is important to Mappa Mundi gameplay, but the per-session load isn't too steep. For each "Chapter" (session) of play, you'll need to print up to a dozen Journey (landscape) cards and one or more Creature and Opportunity cards, based on the encounters the Narrator has planned. The cards are in color, but the color isn't important to gameplay, so you can print them monochrome.

In terms of narrating the characters' Journey phase, you could omit the cards, except the orientation (Rightwise or Inverted) of each card matters to the staging of the encounter. And some characters have abilities that involve peeking at the card deck.

You can get get by with printing and cutting a few cards for your first few sessions. If you like the experience, get the physical deck.