You will find that most people will answer this question by recommending what they have themselves.
A KH is a high spec and fairly expensive unicycle. It would be great to own and ride, but may not be the best choice for a complete beginner. You wouldn’t buy a Stradivarius for your first violin - when you might soon find find that you would prefer a cello.
If you look at unicycle dot com, you will find beginnner’s unis, intermediate, and top quality ones. You won’t get a bad one, even if you go for the bottom end. If you buy from a local bike shop you could get a good one or something really awful.
It is generally recognised that a 20 is the easiest to learn on. However, plenty of people have learned on 24s or bigger. Someone in this forum even learned on a Coker (36 inch wheel).
Every part of a unicycle can be changed and upgraded. If you buy something basic now, you can improve the pedals later, change the seat, get some longer or shorter cranks, buy a better tyre, and so on, as you find which part of this very varied sport appeals to you most.
Some people have lightweight 19" or 20 " unis with fat squidgy tyres and spend most of their time bouncing around on picnic tables and walls. Others have big fat tyred 29" unis (or 36" Cokers) and go rushing about the local forest annoying the wildlife. There are people who ride 24" or 26" unis down steep rocky mountain paths - they don’t so much fly as plummet. Some of us have smooth-tyred 28" or 29" unis and ride on the public road or easy tracks, doing 50 or more miles in a day. Others have a 20" uni and spend all their time doing the unicycle equivalent of figure skating or ice dancing, doing all manner of clever tricks like triple axles and double entendres.
As a beginner, you simply need a unicycle that you can learn to ride. You need to be able to ride it confidently, turn easily, and mount and dismount tidily. If the unicycle is fairly robust, it will then allow you to ride easy unsurfaced tracks, small kerbs and so on. By “fine tuning” it with different pedals, cranks, tyre and seat, it will become better for whatever style of riding appeals most to you. Your second uni can then be exactly the right one, because you have had time to decide what you’d really like.
My first was a 20" with a moderately fat tyre. My next was a basic 26". Within a year or two I had the complete set. I have now narrowed my collection down to four: a basic 20 for parades, a KH24 for difficult MUni, a 26 with a less fat tyre and shorter cranks for cross country, and a super skinny 28" for road and paths.
Avoid lollipop bearings at all costs. Make sure it has cotterless cranks. Buy from a trusted source.