Confirming on the minimum intelligence level, without enough intelligence you get an learning malus, like weariness system, towards how fast your character learns as they need more time to understand the difficult concepts in the book. So as you mentioned it is a soft barrier.

Funnily enough I was thinking the other day intelligence is the stat you take to get into the crafting and maintainence aspects of the game and to avoid as much boring sitting and doing nothing sections as I try to make gear and equipment (proficiency training and gain minimum skill requirements to shorten crafting time)

For a restricted challenge playthough , where you don't worry about crafting, it is still possible to do well as there is npc faction stuff that can cover most aspects - food, shelter, armour, weapons, currency and would work well with a nomad playthrough ( your "intelligence" is then your characters instincts and adaptability to a new world instead of using the knowledge of the past to build your future)