Most of the Admiralty/Department of Transport charts are available at good boating supply stores.  If you are on the cheap, use google earth/nearmaps for the shallow stuff. 

Because surveying the ocean is expensive and there is a big duty of care issue in providing current, correct navigation data you generally have to purchase the charts in paper or go and buy a chartplotter and card with current data. Might be able to get some freebie charts or a secondhand plotter?

I am not aware of any websites offering charts with sea level, navigation marks/hazards etc.

Bryan

Here mate try these sites, just done a search on google for Aussie marine charts, you can't see much from them online but you can buy them.

The ones I have bought do have sea levels, reefs etc.

www.marinedirect.com.au/catalogue/category970

www.hydro.gov.au/prodserv/charts/standard-aci.htm  

www.transport.wa.gov.au/imarine/19100.asp

There are other sites, this is just a start, hope this helps