Oh, good luck with that! You've probably heard this, but Portuguese grammar is super hard. Except for teachers, enthusiasts, and academics, I guess nobody here really knows, let alone explain most of our grammar rules.
Speaking for myself, as a journalist who've written for major outlets in Brazil, I get away with writing (mostly) correctly based on feeling (reading a lot also helps a lot!).
> no wonder it's the third "same" device I've bought in seven years
> no wonder I've bought the "same" device three times over the last seven years
I liked your critique a lot: showing progressively better sentences and explaining why each is better. As a native English speaker learning Brazilian Portuguese, I have the inverse problem of the OP. I'd like to find a book or app that does more or less what you did —— start with a moderately difficult sentence in Portuguese the way an English speaker might say it, then progressively improve it while explaining the reasoning along the way.
Maybe such a thing exists for people learning English; I can confidently say that there is an order of magnitude more resources for people going from Portuguese to English than the other way around.