The problem with Chatswood are the schools. They are amongst the most overcrowded in the Sydney area. Many kids cross the Roseville bridge to go to Killarney Heights.
Upper North Shore is nice. Lindfield is on the train line and I like the concept of their school, the Learning Village.
Not sure about the community feel. Lindfield has many mansions and then on Pacific Highway the usual appartments and shops, but not really a centre with a community feel.
Manly village or Freshwater village have a strong community feel. Freshwater is out because transport would take ages, but Manly with the Ferry + train would get you to Strathfield in 55 min. Little Manly and its gorgeous Collins beach, even Fairlight, away from the busy part of Manly is lovely.
I admit, I am a beach girl, and I love living on the Beaches, especially when it melts with the bush. The Manly to Spit bridge walk is gorgeous or even the Manly to Collaroy walk where you have to walk through the bush at the back of Dee Why and then walking amongst the pelicans on the beach at Fisherman's beach. The Northern Beaches are very different from the Eastern Suburbs beaches. A lot of natural land.
By the way, Dee Why has the B-Line, a new fast bus line with only 1 stop per suburb. But, even with a bus lane, the bus has to go through the Spit bridge and that is at a standstill in the morning.
High School however could be an issues because there are only single sex high schools. Mackellar Girls and Balgowlah Boys, unless they pass admission test to Manly selective.
I know I said forget Mosman because of lack of train, but I didn't consider that the B Line stops in Mosman and schools are great there, and Mosman has a village mentality, albeit a very posh one.
Now going from the beaches to a train station is one thing, but going to the airport might be tricky depending on the time of day. My DH has no issues in the early hours, but he drives there. Anything before and around 7 is fine. Going at 8 is a nightmare.