I am on the Northern Beaches as well. If you commute by public transport to the CBD, you should really stay close to Manly. There are many fantastic suburbs around Manly but if you have to walk from Freshwater to the ferry, it will take you ages.
One word about the Medicare. IT is nothing like the NHS once you have a problem. Your family GP is covered if you bulk-bill in some medical centre. My Gp charges me 82$ and Medicare gives me back $36. My neurologist charges me 320$ and medicare gives me back $70 and the same with ultrasound, MRi, .... and I have a platinum private health care . Specialist doctors and exam are not covered by private insurance. And god forbid you need even a tiny surgery, you will be out of pocket for thousands.
Dentist are soooooooooooo expensive, this is the main reason I have an expensive private health care.
If you don't take private insurance, you MUST take ambulance insurance (around 80$/year) otherwise your ambulance trip might cost you thousands
Car are expensive compared to Europe. You need a double insurance, one is yours, the other called green slip is linked to your registration tax and car, so if you sell your car, the insurance is lost on you. I would say around $1300 a year on registration and car insurances.
Internet is crap. And don't be fooled by the NBN broad band high speed, which is high only on paper and is now buried in a high number of complaints
I am not a big fan of Bondi. My son had his body board stolen in Bondi.
I would go for Manly. Even in winter there is a lot going on, nice bars to have a drink, greet library, bakeries, cafe, there is a pedestrian centre, and I just love Harris Farm.