Another place to get route ideas is the Bicycle Victoria website
www.bv.com.au
Go to the Great Rides section; there should be route maps for the Great Victorian bike rides, also some out-of-state ones inc. Tassie and WA.
>The Grampians are probably not a viable side trip on reflection.
About 3 hours on the train to Ararat, then a 50k ride from there to Halls Gap. We left Melbourne at 8am and were in Halls Gap by 4, having visited a winery. And some of the views up there are just stunning...
Yeah, train to Grampians is a better idea than cycling from the coast.
+1 on the views esp from Mount Zero looking west at sunset (Nb. make sure you leave enough time to get back down before it gets too dark)