I don't think you can actually break anything
As far as I remember what I did was set everything up how I wanted it and then dive into the menu and select the option to save the settings. And that's it.
I normally use aperture priority until the shutter speed drops too low and I then switch to manual with a more sensible shutter speed. When taking people picture I select custom setting 1 or 2 depending on the light levels, the custom setting for aperture with wide are and face detect it the light is good and the manual custom setting if the light levels are low.
If I had an A7c I think I'd have the same custom settings plus another one for manual lenses, as suggested above.
If I were you... I'd stop worry about breaking something and just do it. It is actually quite easy but keep in mind that you will probably forget something and have to redo a custom setting of three until you get them right