Internalize what makes sense to you and chuck the rest. Anyone who tries to convince you that theirs is the One True Way is deluding themselves and you.
QandA
Scripts sold
There are resources for finding out what scripts sold for what, but verifying the truth is another story.
Getting rights to a concept album
Copyright almost certainly rests with the songwriters, so start there.
Being rewritten
Even the most experienced writers with multiple credits find themselves rewritten badly at times. When should you take your name off a movie?