“I think you are being over-generous on the avionics repair capability of the owners”
It took me 550 hours to do my panel and wire my aircraft, this included learning how to as I had never done it before. I did need a few hours of help with the navcom, which was too hard to work out. However, the glass home built stuff is relatively easy. Firstly, the kit is intended for home installation so the manuals are simple and straightforward. Secondly, you are not “fixing avionics” you are swapping/isolating modules. The LAA run courses to teach all this now, but when I did mine this was not available.
I used this site, which I found useful for my original build;
AeroElectric Connection - Aircraft Electrical Systems
“but also you are a competent mechanical engineer and a competent electronics engineer ”
I will leave Choxolate and others who have seen my creation to judge that.
Rod1