(not a teacher)
1) I'm not familiar with this use of "idyll". I know it as a type of poetic or musical composition.
2) Honestly, you could use any of these words, but I think "cosmopolitan" is the most common collocation, if only by a slim margin.
3) I want to say it's "assertive", but "urbane" and, to a lesser extent, "urban" could work, too.
4) "Civic" is the best choice here.
5) "Dwellers" is the most sensible choice, though I don't think "slum dwellers" would ever be my first choice of words for expressing that concept.
6) Either "rustic" or "pastoral" will work well here. A case could be made for "rural", but "provincial" is a bit derogatory.
Gillnetter, they wouldn't think you were talking about an idling engine over here because of the pronunciation. It's not "eye-duh-l" it's "idd-ill" or "idd-uhl", the same as the pronunciation at the start of "idyllic" is "idd" not "eyed".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
Yes, I could have and I am sorry that I didn't. However, I like seeing you discuss the language. It is ever so educational :) Once again thank you and please do not get angry with me. Lesson learned!