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.
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.
Forget everything you know about driveways.. Asphalt, concrete, crusher run gravel, rail road ballast, paving stones… If you have a long driveway, or if you need a system of driveways on a farm, and you are planning to go with those common methods of paving a driveway, you are going to need a separate mortgage just for the driveway (or driveways).
Performance wise it is going to be middle of the road, like most tubs it only has a few of the expensive hi flow therapy massage jets and lots of the inexpensive smaller jets, the neck jets system is pretty much non-existant you really need the mid flow jets at least for big muscle masses like shoulders.