I really wasn't sure about question #2 on this one ("太阳从 ___ 慢慢落下了"), because I would have expected 从 to refer to where the sun came from rather than where it's going...
Yes, I thought the same thing! I looked up "太阳从西边落下“ to see if I could find anything, and the phrase...seems to exist...but not very much? As you say, 在西边 does seem to be a possible alternative. Not sure if the mandarinbean site made an error or if it's just an odd expression.