People use emotion to buy a bike and logic to rationalize it. So nothing I say will change anything...but here's my opinion. For your first bike, get one you can handle easily and that is used, cheap and popular !!
Realize that you are probably going to scratch it. You're almost certainly not going to keep it. And your tastes will likely change with experience. Also, it's easier to get test rides on used bikes. So don't become "target fixated" on a new, expensive first bike!
Once you've got your bike, go out and practice every day. If you buy an expensive first bike you'll be reluctant to practice which will limit your riding skills for the rest of your life. After all that, you can buy whatever you want with a good chance of life-long success. It will depend on you, not the bike. The operator is the dominant safety device for a motorcycle.
As for size of bike, I think the main point is to get one you can handle well. Most people become fixated on one or two bikes and don't test ride enough different types. Bikes vary quite a bit. Some are top heavy, others not. Some are high while others are low to the ground. Some are touchy with the clutch and throttle and others aren't. Some are close to the handlebars and others feel further away. Some a great around town and awful on the highway. Some feel heavy, others feel light. Some kill your wrists, others kill your back. And still others kill your bum!!! Don't be timid, try them all out. It's *your* money. You'll only buy a first bike once so have some fun with the experience!