First thing engage a building surveyor. They will give u a list. You can also look at the national construction code on line. It has the list of requirements for dwellings

I've talked to a couple, but I'm a bit cagey about engaging (paying) one before I know what I'm getting into. One that I was quite keen on working with has repeatedly tried to insist that he needs to be involved if I'm doing slabs for <10 sq m garden sheds, ignoring me when I link him to the VBA saying it's not required.

And none have been forthcoming with a list, so I'm assuming that's something I'd get access to once I start to pay them.

You’re putting the cart before the horse. An OC comes at the end of your building project and ensure that you’ve complied with your building permit. And to get a building permit you need a planning permit. The local Council will issue the planning permit. I’d start with the Council website. And most Councils are happy to advise you in the feasibility of your project over the phone. And you will need a planning permit for a shed >10sq metres. It is the planning permit that determines what type of dwelling you can build on your land. On a base level you will need to connect to sewage and stormwater disposal if it’s available or have Council approved methods of disposal if not. You will need a kitchen and some sort of laundry with a trough. And toilet and washing facilities. There will be minimum and maximum sizes of dwelling for your land. In some areas the power distributor requires you to pay a service fee even if you don’t connect to the poles. And connection to the poles can be many thousands of dollars depending how far away they are and if underground connections are required. There are forums on the web for shed dwellers, small houses and off-grid properties - worth googling and reading.

I'm lucky enough to not require a planning permit to build a dwelling in my zoning, albeit with various caveats like setbacks etc. I think I should explain that the cart I'm trying to size up (to use your metaphor) is the budget for the project, in order to determine if it's viable. The OC is the end goal of the project, and therefore defines the size of the cart (budget).

Sewerage will be septic, as the town has no reticulated sewerage. The stormwater plan that council gave me only showed drainage pits uphill from me, which makes sense as I'm downward of the rest of town.

I'm required to connect to the poles, and when I do so will be determined by budget and of course OC, but I'm expecting to pay up to $10k based on a provisional quote from the supplier. Good info to know abuot washing up facilities etc. I'm guessing a bath/shower is included there? I've been unable to find a minimum size for dwellings, but there were some provisions about the minimum amount of "private" space behind a dwelling.

I'll have a look for these 'shed dweller' / small house type forums. Do you recommend any?

to comply with our Council regs and BASIX we built a small fully lined and insulated steel house that includes a separate bedroom, bathroom, laundry and combined kitchen living area...total 49sqm plus attached ënclosed carport that can be converted to extra living area...our regs required fire shutters, 65.000L water tanks and a septic system equal to a family home and the building has double glazing, AC, air sourced HWS, tiled bathroom, fitted kitchen, stove and washing machine.... total cost was about $150,000 but that includes substantial earthworks and all labour and that could be a big saving for you...we invested more in the building because we have a very comfortable holiday home that we could sell as a house rather than a building that is not a legal dwelling