Has anyone done a renovation as an owner/builder?

We are planning a balcony extension plus an extension to the kitchen to add a room, the guy who did our bathroom wants to do it ( we trust his quality of work) as the project manager and use people he knows for the carpenter work etc, and have us register as owner builders.

We trust his work etc but we are a bit clueless in this stuff, so are paranoid that we will be taking too much of a risk insurance wise and we aren't rally sure if it is even legal to do it this way.

Any advice?