You'll be fine using screenings. In the shady area moss will grow in the screenings, in the sunny area, maybe not so much. If you want you can promote moss in the shady area–put some moss in the blender with old beer/buttermilk (perhaps this is what you mean by the "yogurt method"?) and pour the slurry atop the screenings to get the moss to grow there.
Your cat salesman can show/give/sell you the "Caterpillar Performance Handbook" i think that's the name - it has operating cost data with all the variables for your operating conditions - should answer most of your questions on your cat equipment.
A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust.. Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of or recycled, or to reduce the size of a solid mix of raw materials (as in rock ore), so that pieces of different composition can be differentiated.
This DIY article; and the rest of the how-to section of my blog, cover much of the basics of how-to properly build flagstone patios. These articles offer general guidelines, or suggestions at least, that will be of much use to the hobbyist, DIY landscaper/builder, and to professional builders as well.