Thanks, that makes things a lot clearer for me.
I also agree that in 9' it makes sense to move "organizing..." to the front. However, would it also be possible like this:
9''. A popular spot for the youth, organizing a wide range of activities throughout the year, the community center is a great place to hang out.
--> Could "organizing a wide range of activities throughout the year" here be seen as a reduced non-restrictive relative clause that postmodifies "A popular spot for the youth"?
11: The house is only a 5 minute bike ride from the school.
--> I would say "only a 5 minute bike ride from the school" is one NP? Is that right?
And is there a difference between postmodifiers and complements? e.g.:
12: It is the dream of my father to travel to China.
--> Is it right that "of my father to travel to China" is a complement instead of a postmodifier? Or are complements a type of postmodifiers?