Native German speaker: Most of the time we think it's just funny if you get the gender wrong, no harm done. As you said, there's very few instances where there are words changing meaning if you swap out the article. And even then, it's ususally obvious from context. (Der Schild => the shield; Das Schild => the sign). I do get the frustration though, I had to learn French in school and I'm currently learning Swedish (I'd consider their en and ett words something conceptually similar to the gender thing).

I also agree about mapping the prepositions, but I think that applies to learning other languages in general, or at elast, more than just the pairing German/English. I can only compare it to English => Swedish (I had not interest in learning French as a language, I was more trying to get a passing grade in it. And I do have to learn Swedish from the English perspective, because Duolongo doesn't offer a German => Swedish course), but it's the same thing