@piponfishing@sunbeam.city well, 3 levels would likely make it easier to collect the compost at the bottom... and as you know you need some space underneath for the leachate.

I use worms in a variety of ways, so it's difficult to say exactly. I have little worm towers around in the garden and in a barrel (I wrote about it in a toot a while ago), and I also add them to the regular compost.
My "head quarter" is a 220 liters barrel, it is a bit tiny as they are a lot, but I keep giving them out to friends and more towers. I posted a picture of it today.

As for how much to use, I'd say consider how much you want to grow and eyeball the organic matter you need for it. If you produce 20 kgs of lettuce, you are fine inputing 20 kgs of kitchen scraps + carbonium in whatever composting method you use.

Those shelves look a bit tiny to me for mushrooms... can't you hang some bags to the ceiling or something? You can start with a simple mycelium syringe, or even with some store bought mushrooms and clone the mycelium at the base, it just makes things slightly more difficult.

Consider, as a rough conservative idea, that you'd get around 1/5th of the spawn. So 10 kgs of hay > 2 kgs of mushrooms