The grid LSALT is 8700 ft. This would give you a VFR ICAO level of 9500 ft. It will be cold up there. Wear warm clothes. The heater muff on a single is not necessarily as effective as you might want. A blanket for passengers might be smart.
A carburetted, normally aspirated single will need a fair bit of power up there. Winter will help you out with density altitudes, but you may be needing a higher power setting for the cruise (if you have a CSU) than you are accustomed to. Cruising altitude will almost certainly be above the freezing level, but watch carb icing going through the lower levels.
Make sure that your EPIRB is sorted & current.
In a single, its actually the leg Cooma to Merimbula that would have me more anxious. It gets pretty rugged & remote.
VHF coverage around Merimbula can be patchy. Don't be stressed if you lose VHF comms for a bit. You can also get some wind shear coming over the hills west of Merrimbula.
Outbound from Moorabbin you'll probably be via Eildon. This area gets some of Australia's worst weather. And you're right in the CTA J-curve going opposite direction to IFR traffic coming into Melb. I reckon I'd be paying the money and filing a plan.
I wouldn't be trusting the TAF's. I'd phone BOM for an elaborative briefing.