A ferry is probably your best bet, or from Luna park👍

Sorry, I cannot help you with that one. Try the local tourist office.

Yes the earlier the better to find a spot and reserve it

It is fun & lots to do in the Harbour.

You can get on cruises pretty quickly as there are a fair few operating with some having shows etc We have been a few times and easy to get on might wait for 30 min to hour. The ferry is also another way of seeing lots of the harbour as can stop at various points for photos and is very inexpensive. We were surprised how much we saw on the ferry’s. There is lots to do zoo, museums, restaurants, live shows, underwater world, Luna park for kids, casino you will be able to get lots of information from circular quay or darling harbour. There are lots of short trips on buses and trains and if you search what’s on in Sydney will give you lots of options for sight seeing or thrill seeking depending what your into. Hope this helps Regards

For the opera house and bridge photos, Take the Pyrmont Ferry. You get good views of the opera house from the water. You actually go under the bridge, and get the iconic view of the opera house below the bridge at two of the stops before Darling Harbour. For passing shots of the opera house and long shots with both the opera house and bridge take the Manly ferry (this trip will also provide you iconic shots of the harbour, Sydney heads).

There are 3 wards for international cruise ships that I know of being Circular Quay, Darling Harbour & Garden Island. If it's a local cruise you are looking for then Circular Quay is where most of the Ferries & Cruises leave from.

Yes, you have to book in advance! It is quite expensive, about 300 AUS$. More details here bridgeclimb com Please check my review, I also listed other options for a cheaper great view.