Hiya Jake
You have already made your decision, so I am not going to have a go at you. And you've at least had the sense to get the gixxer legally restricted which is more than can be said for some posters we have had on the forum.
My concern for you, though, would be twofold. People's natural ability to handle a bike varies. That is in the lap of the gods and as I don't know you from Adam there is no point in debating that. So first of all, no-matter what your abilities are, acquiring the skills required to deal with the thousand and one hazards you will encounter daily on the roads as a motorcylist is down to experience, and that takes time. And while you are acquiring it, it is as well to have a machine that is as close to foolproof as possible.
The second concern is that it is pretty universally agreed, by riding instructors, by racers and road bikers alike that the only way to develop your skills to the maximum on a bike is by starting small and working up. It is only by gradually learning to take a lower powered machine to its limit that you will gradually acquire the confidence and ability to be completely safe out there - especially on British roads which are some of the most congested and therefore the most hazardous in the Western World. Without those skills you will never be as safe as you could have been and the likelihood is that you will never enjoy your riding as much as you might.
And while I think it is brilliant that you are already thinking about doing some advanced rider training (go for it!), organisations like the IAM or ROSPA will not teach you how to handle a bike skillfully or well. All they will teach you to do is to ride at maximum speed within the law, obeying basic safety rules.
The testosterone issue is also a significant one. Even at my age mid-50s I still get the occasional testosterone urge (what there is left of it

) It is something that is very hard to resist on a large F-O motorcycle - even a restricted one and even if you are the most sensible person in the world.
You'll have to forgive some of us for doubting your sincerity when you say you intend to be a safe and careful rider. I'm quite willing to believe that, at some level, you are being perfectly honest with us here (I wouldn't say that about many a squid on a 1000cc motorcycle I've read on these forums) But we - all of us -
choose what we want to believe about ourselves as well as about others. I've never come across a young rider yet who was itching to get his leg over a supersport as quickly as possible who hadn't convinced himself that he was either gods gift to motorcyling humanity, or endowed with more than the usual amount of good sense and a desire to be extra safe on the roads.
It is worth remembering that our self-perceptions are not always accurate.
With that in mind, take care. I hope you enjoy your ride.
Stay in touch.
Richard