That was me a couple of weeks ago. Just keep at it. One of the things that was really informative as I started going longer stretches (a city block or two) on the bike path at a time was to be able to feel that the wheel was getting progressively ahead of or behind me and correct that by changing my pedaling rate temporarily to recenter it, then returning to whatever speed I wanted to be going.
Everyone does. It helps to get your arms out to the side. My early attempts that managed to survive the first mistake involved a lot of “arm swimming”, and I still find riding with a hand on the seat handle (after mounting or transitioning from hops) difficult. It’s also interesting to experiment with torquing the tire using your body - oddly it feels like that was a key early on, though I’m not aware of still doing it.
Once I got so I was sometimes stable at all, I started trying to do laps of the lounge area at work. At first I could only make the first turn, then made it most of the way around and finally a complete circuit. The second challenge after maintaining balance was extreme leg fatigue, but it has gotten better: Beginner Struggling to Relax. Getting the seat up makes a huge difference too.
Not having yet ridden a tire like yours I can’t comment if that is ideal, but apart from that assuming you can get the seat high enough (it’s often set lower for trials) it should be fine. Put it this way - if you had a typical learner unicycle, inside a month you would really be wishing you had that KH you scored instead. Wanna trade?
After taking my learning 20" out to a bike path and feeling lost in the wide open space pedaling like mad on my little (word we don’t use here) toy, I ordered a 26 road unicycle. Given how much seat post I have exposed I would guess you would fit on it (vendors often list a minimum recommended inseam, but there are people shorter than you who have ridden 36ers). It does ride more smoothly and with less effort when I finally get going on it, and I’ve actually had more success trying to freemount on it as it stays in place better. But I have to say I still find it a lot more intimidating - my longest distance so far came in part because I wasn’t looking forward to trying to get down, though in reality that part went fine when the nice stretch of path ended. Generally though I’m happy riding the 20" in laps around in the office, but the 26" still feels too big indoors to do anything but try to get on it without support and pedal a few revolutions to prove I’m stable.
You can always start watching your local classifieds for a deal on a larger unicycle, but I don’t think you need to go out and get one yet. Especially if you have nice areas to ride around in circles and work on skills, rather than feeling like most of your options are narrow paths where there’s not much to do but ride in a straight line.
Perhaps, but there are a lot of us who started well into adulthood. The primary issue may be that we have more developed instincts towards self preservation. And longer healing time when muscled get wrenched in panicky reaction to the unicycle doing something unexpected - something that should improve when control ends up being achieved by applying invisibly small corrections earlier, rather than desperate ones later.
Something else you can do that’s worth starting early as it changes your relationship to the unicycle is to find a nice support aid, get your cranks level, grab the seat with your free hand, and learn to hop a bit. Experienced people will say not to treat it as a pogo stick… but I think maybe you have to start out that way, and slow down later.