I agree with OP buy the N9 “based on what you like and what you need”.
Here in Canada the 32GB is $100 more than the 16GB version. $100 for an extra 16GB in my opinion is just down right greed. The N6 on the other hand is only an extra $50 here to double the storage from 32GB to 64GB...
The N9 "mirror" on a large screen using N9'scast screen to Chrome will be 4:3. If your large screen is 16:9 as most TV's/monitor's are these days then you have black bars on either side of the mirrored image.
Yes it worked for me. I have Chromecast and was was able to cast my N9 screen to the TV. My N9 screen was mirrored.
Build number: LRX21L (system says I am up to date)
As to how good it was that's a whole different topic.
4:3 cast to 16:9 TV not worth the bother in my opinion. Black...