Your questions are indeed the most challenging ones to answer. :)
밤하늘은 화려한 별을 수놓았어.
This translation is actually very good. The personification of the night sky is very poetic and fresh.
I'd say it's much better than what most "professional" translators would do.
Replacing 화려한 with 찬란한 would be a good idea though since 화려한 doesn't suit the stars that well.
밤하늘은 찬란한 별을 수놓았어.
That would be it if it were about sounding poetic. But if not, then a less poetic version is due:
Let's stick to the passive nature of the original sentence.
밤하늘에는 찬란한 별들이 수놓아졌다.
That above might seem viable at the first glance, but we have a different logic. It focuses on the verb "수놓다"
Therefore, it sounds as if new stars appeared recently.
밤하늘에는 찬란한 별들이 수놓아져 있었다.
That would make a decent translation.
Let's go for the authenticity now.
Stars aren't something that can be embroidered. For figurative expressions, we resort to "as if"
밤하늘에는 찬란한 별들이 (마치) 수놓은 듯 뿌려져 있었다
밤하늘에는 찬란한 별들이 (마치) 수놓은 듯 빛나고 있었다
That's how I'd translate it.
뿌리다 = to sprinkle
뿌려지다 = passive of above
빛나다 = to shine/to gloze