Flying direct Moorabbin to Merimbula will take you well south of most of the larger hills like Buller, Hotham, Falls Creek (Mt Bogong and Feathertop) and Kosciuszko. You path will lie closer to BawBaw, the terrain through this area is still very rugged with high IFR LSALTs behind Bawbaw and forced landing areas are extremely limited anywhere in this area.
As the others have said plan for the worst make sure you have warm/wet weather clothing available and survival equipment, especially some extra water, food and locating devices. No radar coverage and unreliable VHF means at low level if you go missing they will take a long time to find you. Make sure your mobile is fully charged. Below 10000ft there is little radar coverage outside of 100nm ML, less if lower.
The weather can change rapidly and be vastly different over a few miles, so using an AWS or TAF from YHOT is only good for that point, even 10nm away it is next to useless.
The ranges west of YMER can be a trap for VFR, the cloud often covers the tops and will not be reported on the Aerodrome TAF or AWS. Merimbula being on the coast the weather is mostly pretty clear there, but not the approach through the hills.
Do not fly down valleys in the hope the cloud is the same height all the way through and you'll come out the other side remaining VMC.
Have plenty of alternates like Sale, Albury, Bairnsdale Etc.. and make sure they stay easily available as you progress. A cold front approaching from the west can cross the entire area in a few hours reducing conditions to barely safe for even IFR.
If you are IFR capable remember from this time of year and through to pretty much November the freezing level will be as low as 3000ft. Any flight into cloud will result in serious icing at levels above FZL especially at 6000-10000ft.
If you do intend this sort of flight at this time of year don't lock into accommodation or activities that will give you incentive to press on. Wait for the perfect conditions and be very cautious.