On the other hand, using this as a baseline and evolve from there will save a lot of time. I mean git conventions are starting to sound a bit like tabs vs spaces, just with a lot more options.

Pick a standard example, go with that, evolve. Same with e.g. processes, pick e.g. scrum, do it by the book at first, evolve.

I've started at half a dozen projects and every time a huge amount of time is being spent (wasted) on reinventing the wheel, be it processes, version control, code style, etc.

You're correct. There are more fundamental conditions that have to be met for effective collaboration.