There’s no ‘right’ or ‘wrong’ place to start.
If you wish most of all to stop wasting water then make that your first project, if you want to use the sun’s free energy, then install solar.
BUT: have a plan that simply lists your priorities in the order you’re keen to proceed. Then do your best to ensure that doing one priority does not undermine another priority. I’ve made and continue to do some things which could have been done differently. But I did something rather than nothing.
Key lesson? I learn by doing. It makes me see more clearly, helps me to reflect and to learn, to ask specific action-related questions.
Make a list of your top ten priorities and see whether you include any one or more of these: use rain water, recycle water, self-sufficient for energy using the sun, wind, good design, non-polluting and local materials recycled where possible, pre-fab construction to save costs, waste, time . . .
Have a look at this article and the short video there
There is a model of my house in a permanent exhibition at the Powerhouse Museum on sustainable design and materials that’s worth a visit; https://maas.museum/event/ecologic/
Visit houses in the forthcoming national Sustainable House Day, 15 September, 2019, particularly any which may be open down near your site: https://sustainablehouseday.com/about-shd/
Seriously investigate potential for prefab; there are many options - eg https://how-nanohomes.com.au/
Water and energy are easy, as is recycled blackwater and grey water but approvals for blackwater recycling are difficult as local councils are poorly educated and staff have little to no training;
Look at the mistakes I’ve made and published in my books and on my blog and avoid them if possible;
I’m passionate about recycling everything - material, food, and so on and if you wished to commission me to either project manage or get approvals on recycling grey or black water then I’m keen to discuss that option with you.
Most important of all:
Do NOT sign a standard building or design or architectural or engineering contract.
Instead make a contract which has at is heart your ten or so priorities and specific goals and make payment of your team members dependent on them delivering those.
Do NOT make a contract with anyone who will not accept that you’re paying them to give you that list of priorities.
Most standard contracts are confined to saying what the contractor will do and how they will be paid and do not put the client’s goals at the heart of the relationship.
Hope this helps,