Probably the best way to practice for riding a 36" in high gear is to ride around on a 54" unicycle. If you happen to know someone who has one. I was fortunate in that I had a 45", and I used to have a roommate who had made himself a 50" and 56" wheels.
Not sure who you are writing to, but those giant paragraphs were a mouthful. If it’s to a vendor I highly recommend separating out each question on its own, and providing an itemized list of what you want to order.
I don’t have an opinion on the various clamps mentioned, though I recommend a non-QR, double-bolt one for any road unicycle with a long handle. You can put a lot of torque into a seat post with a setup like that.
I have mine set up curve down. The brake lever is under the bar, so that would seem the better direction to protect it. But my brake lever is way back toward the seat for upright-seated braking. My Spooner lever is nowhere near ground contact.
The alternate is a different piece of tubing. My inelegant solution is a simple BMX seatpost. It’s chrome and it fits, which were good enough at the time. I added a BMX handlegrip to the end of that, and had me a MUni handle. The purpose of that handle is to be there instead of my beautiful, custom powder-coated Shadow handle for the trails. But yesterday I did several miles of (easy) trails and didn’t even think about having my nice handle on there…
That will be good discipline and force you to learn your high gear skills faster, but you might find it frustrating.
You won’t regret choosing the KH frame; I love mine and never a hint of slippage or bearing issues.