This is the one point I will disagree with you on.
Maybe in certain genres starting with something else works, but most music is composed melody first. Actually, starting with a chord is still technically melody first.
Great example being that the very basis of part-writing, and how harmony came to be understood today, is by playing multiple melodies at the same time. That's all a chord really is: Different melody lines moving homorhythmically. Pretty much everyone from Bach to John Williams started with a great theme or motif, and harmonized it from there.
Not to plug my own shit, but I literally just posted a track for critique over in the Original Music forum before reading this. I started with all the melodies, and built from there. To my ears, it turned out cohesive.
So I'd agree that building a piece of music is like building a house, but I'd disagree that the melody shouldn't be the foundation.
EDIT: Points 7, 8, 12, and 20 are very, very good points.