Welcome. It's great to hear that you're doing this in a very methodical and rational way. Kudos to you. It will pay off in the long run, I can assure you.
The only thing you did wrong (in my opinion) was to buy a new bike as your first. However, the principal reason for recommending a cheap, secondhand bike at first is that most people, whether they plan to or not, do most of their falling off in the first year or so, and it's cruel to do that to a new, shiny bike
Your attitude mitigates that risk though. If you're as measured and sensible as you appear, you should be fine. Besides, I still manage to do a graceless topple from time to time even today, after decades of riding much bigger, heavier bikes.
Another piece of unsolicited advice now
If you get hooked on this two-wheeler malarky, as I hope you do, you will want to move up onto bigger, faster or just different bikes in a year or two. DO NOT be tempted to leap too many categories. Many new riders will jump from something small and light to a litre bike, or a supersports 600, and this can not only lead to trouble, but can actually put you off bikes because you struggle to adapt to such a big jump. Make any steps 'up the bike chain' in modest increments and you will actually find you grow better as a rider.
If, on the other hand, you stick to your beautifully light and manageable 300, you will still have lots of fun. Enjoy!