Couple of points from a neighbor from Lancaster county.
First, don't reinvent the wheel when it comes to a foundation. You live in an area where shed manufacturer's are everywhere, and used a common platform for their products. Basically it involves treated 4"x 4" skids, or sled runners, with floor joists, a rim joist and tongue and groove plywood subfloor completing the floor system. If this is placed on well drained gravel, AND the structure has gutters and downspouts, it will last a lifetime. When it comes to shed manufacturers. you might want to think about visiting a few and getting quotes on a basic shell of the building you are looking for.
As a retired builder, I know that we live in a unique area. There are so many Amish manufacturers in the state that building your own smaller outbuildings can be an actual waste of time. I have a buddy in retail lumber sales. At least once a weekend he has a homeowner show up with a lumber list to price, for their shed. He usually replies with, " You can figure that EVERYTHING to complete this shed will cost you X per sq. ft. and, as a novice it will take you at least 50 hours of hard work until you are done with the roofing, painting, building the doors, etc....... Once you get my lumber list, price the shingles, windows, door hardware, etc.... you will end up at the local shed dealer and discover that it's way cheaper to buy one, even if you don't value your time all that much. Do you still want to wait a few days until I can get you a price for the material? I fist discovered this decades ago when one of my carpenters decided to build one. We priced material and labor, and discovered that the shed manufacturer's delivered product was about $4 a sq. ft more than my cost for the delivered material.
As for DIYer, you need to really get a handle on costs before you go too far. That opening window wall on one of your pics. could easily run $6-8K. The giant, oversized, commercial grade sliding door could be $3-4K. IMHO, I would simplify the design by eliminating big overhangs and glass that wraps the corner. Then figure what type of windows/doors you can live with in a fairly low budget. To put this in perspective, a standard vinyl window on most sheds and garages will run $100 or so, and a steel door, less than $200.
As for some other questions, I would frame it with standard materials, including nails. I would insulate it with Roxul and use spray foam cans for air sealing, of windows doors and other openings. I like the designs you posted, but if you want it to last, you are going to need a gutter and spouts to get the water away from the shed. If you talk to a shed builder, or dealer, they will tell you that the #1 reason that sheds fail is that they get wet and stay wet. Most don't have gutters and the water hits the gravel below and splashes up the siding. I't common to see a Craigslist ad in this area for a "Free Shed". Typically it involves the lucky winner hauling a rotted shed away, and the pictures show siding that is typically rotted, or even missing from the lower 18" of the structure.
Finally, even with a major rethinking of the window/door situation, I could easily see this project hit $6-8K in materials alone.