Now you've done it :I'll have to add my native 2 cents ;)

I agree with all your remarks, except (5) is more like "couldn't" meant as "did not manage to" ("did not know how to").
Another case of headache with savoir/connaître and their many fuzzy meanings :)

Il paraît que -> that's idiomatic for "they say..."
"à ce qu'il paraît" would be like "or so they say"
Another possible variant is "on raconte que..." / "à ce qu'on raconte"
"it seems to me" would be "il me semble que" or "j'ai l'impression que..."

Elle me dit -> that could be simple past, but that tense is too literary for this song. It's clearly present tense.
The past would be "elle m'a dit" (told once) or "elle me disait" (used to say)

Elle en a vu des... -> this en..des construct means "so many/much" (she saw so many moods - whatever that might mean !)
J'en ai vu des abrutis, mais des comme toi... -> I've seen my fair share of idiots, but rarely as stupid as you" :)

"humeurs" is sloppy French. "saute d'humeur" would be a mood swing. That's clearly what they mean here

J'en ai commis des erreurs -> more of the same (I made so many mistakes...)

Elle qui voulait -> that's a French thing, just an emphasis. A direct translation sounds like English-painted French :)
"All she wanted was..." or something like that.