Honestly with the cost of sea freight exponentially high over the last few years I would seriously hesitate. Place like Geneva if it is only 2 years then rent furniture. Plenty of bikes to buy the second hand.
It's a huge cost. I have moved a container all around Asia, this is it's final resting place, never again.
I have applied for a COE to get to Pattaya, but same process. your COE is just the permit to be allow to arrive and enter Thailand, it does not specify a length of time, your Visa does this. You can apply for a COE specifying to the embassy you wish to use the visa free 45 day entry. Once you arrive you can start the 30 day extension.
flights... technically you must have a flight in and out of Thailand. some embassies look for both, as mine did in Jakarta, others didn't. some people use non-genuine flights tickets ($5 online) to get the exit flight, but I am not advocating that, i am using a one way in the Bangkok and an exit flight fully flexed with Emirates to Dubai that I can extend for a year at no change.
So.. 1. start the COE, get the first stage approval.
2. get a flight out
3. Get your vaccinations sorted (both for sandbox)
4. Get your SHA+ hotel Sorted
5. Add all of this to your COE record, and get final approval.
the only part I cannot confirm is how you get permission to leave Australia, but as previously stated if your leaving for > 90 days you just tell them that...