You need to know enough to evaluate the care you are getting in a boarding barn.
I agree, longeing and other ground handling skills are skills you can pay your coach to teach you.
I think you are rushing things a bit if you have never ridden outside of lessons, even in an arena.
I suggest you first do a half lease of a horse on your barn or at least pay to do practice rides outside of lessons. If the barn thinks you are still too beginner to do that, don’t get a horse!
Also have you thought about whether you have the time and energy to ride 5 or 6 days a week with your own horse?
The next logical step for you is a halfease or paying for practice rides without lessons 3 days a week in addition to lessons. It’s really important to make that move because you need to learn to set your own routine on the horse and become self directed.
Some of us find lessons a necessary evil and are happiest riding alone. But I’ve also seen beginner riders especially kids get very attached to the highly directive group atmosphere of a riding lesson and feel a bit lost without a coach. Realize that most advanced adult riders take at most one lesson a week, sometimes once a month or even less frequently. You need to make sure you feel comfortable riding alone at least in the arena before you take the next steps.
If you have never been on a trail ride I suggest you find a local dude string and go out for a guided trail ride. You will not get to do much “riding” and will be a passenger mostly. But you will get the feeling of being out of the arena.
Many competitive riders never go on trails or hack out. They feel their horses arent safe, they themselves are a bit agoraphobic about trails, or they find trails boring. I grew up trail riding and love it, but it is very different from arena riding. And you need to be in control of your horse