Happy weekend everyone.
I’m looking for advice on commencement of building a medium sized extension in Adelaide. The house is a 1900 villa with a daggy 30sqm southern facing lean to. We intend on repurposing this area as bathroom, laundry etc, adding a 50sqm multipurpose single room for kitchen and living behind it, with a carport to the side.
Alongside an architect we have developed a concept that is now being moved through drafting and private certifier, and council initial stages. Ideal timing is commencing construction next year. We intend on moving out for this. We are hedging bets for delays and not being ambitious with respect to “must be done by” and have somewhere to live for the duration.
I’ve approached a few smaller builders locally whose work looks good or who people have recommended. The figures and ideas are drastically varied.
We have used a carpenter/builder previously who has done major work within our family including second story additions, and I approached them about this. I have trust and respect for this person.
They have expressed a keenness about the project but have lost faith in some of their go-to people within some of the trades after some have retired, and based on this have expressed reluctance to be the nominated builder. We have used most trades required in various previous projects, except cabinetry and bathroom tiling.
The carpenter/builder has said they can project manage on site and work with me on timing and organising everything, as well as manage carpentry.
I’m not sure about how this works. Implied here is that I would be an owner builder, as no one is going to put their license on the line and pass management to a third party and trades not known to them.

I’m not experienced in building management. As far as SA owner building goes, what steps are practically required if we were to self manage the process?