Madang to Wewak via the Hermits is a great trip. There are a number of great sites in Madang and on the way and Craig will take you to all of them unless of course the weather conditions are unfavourable. You will most probably be diving some new unnamed sites also which is always great fun as there has always been great pelagic activity out that way.
How long are you in Sydney for? I used to live there and absolutely love the place as there is always so much to see and do and fantastic places to eat! Here is a link to a good site which should be helpful
http://www.sydney.com.au/
The Golden Dawn is very comfortable and if it does get a bit "roly poly" the stabilisers work quite well. You'll have a great trip, try and get cabin 1!
Happy diving!