Here’s the major thread on mushrooms.
To make the living soil, you can use spent cakes from grows, or you can add fresh spawn and grow your living soil. You sort of have to get basic shroom growing down first, because getting the mycelium growing, uncontaminated takes a base level of familiarity.
I would make spawn jars, and then colonize a bunch of coir, then add the colonized spawn/coir combo to your soil and then let it take over the soil. You want carbohydrate in the soil, lots of it for the mycelium, but not so much that your plants get too many nutrients. I err on the slide of too little. You can always add stuff later.