Good morning seahorse1,
I love it when I dig in and learn something new. Your points about the name Lucifer are right on. The Hebrew heylel means day-star or shining one, and the Latin Lucifer really has no business being in an English translation. Tradition is a powerful thing, often for good, but not always.
But I don't know that I would be dogmatic about the Isaiah passage being only about the king of Babylon. I believe it's one of many passages in Scripture that refer to something earthy, here and now or near future, but that are also talking about a bigger picture idea and/or a far future event. Christians are not unanimous in their opinions about this passage (shocker) but I see value in reading it also as a description of the sin that caused Satan's fall. Thinking of it this way, some phrases fit an earthly king more (such as going to Sheol) and some fit Satan more (such as "make myself like the Most High"). And stars represent several different things in Scripture, of course.
So thanks for posting, and I look forward to future conversations.