Don't sweat it too much. You'll come, you'll figure it out.
You'll need long term visa to do long term stuff, driver's license, bank accounts, etc. But you won't need to figure that out right away. I would get a tourist visa maybe METV and travel around Thailand and abroad, find place you like, find people you like, ask them what they do. The right answer will come to you.
Thailand has two season... Hot and Hotter... You will not need to worry about the cold (unless you go to the high country in the North).
It's possible to drive but more comfortable not to drive. I am also a US citizen and drive a motorcycle everywhere (including Bangkok).. I drove a car once in Thailand and hated it. They drive on the other side of the road, which isn't so bad, but you'll find that the windshield wipers come on every time you use your turn signal (... because its on the wrong side of the steering wheel). The driving customs are very foreign, confusing, signs are in a language you likely don't read, google maps helps only a little and less at 60/mph, and generally a pain in the ass. Eventually you'll get it figure out then you will go home. In the end you will have traveled half way around the wrong and all you've done is learned to drive on the wrong side of the road.
From BKK flights to Phuket are cheap, there is a train that can take you most the way (I think), and there are buses or if you want to spend the bucks you could rent a private car/driver. If I felt the need to go to Phuket from BKK by land, I would take a bus from one town to the nex, over the course of 2-3 days.
My first license was a couple of years ago. I don't exactly recall everything I needed but I do remember it's a pain in the neck.. Doctor's letter, class/instructor letter, immigration letter.
I found someone who helped me get my second license... It cost me 3000, took me 30 minutes.
My girlfriend and I have no issues going up steep hills. Together we're 120kg.
Top speed without the girl is about 100-120km/h. That's fast enough to hurt yourself pretty good.
Scooters are good enough to get through the city without issue. They're not so great for long trips, off-road riding, or similar real motorcycle activity.
I have rented motorcycles in several SE countries. There almost always have a Click style motorcycle, named something different. Given the popularity of the bike I doubt they'll discontinue it anytime soon. They may rebrand it but I am skeptical of that.