There are possible worlds in which God does not exist, therefore God it not necessary.
Yes, from nature. We evolved as a social species, If you look at all of the moral behviour that transcends culture, it usually isn't limited to our species. These universal moral behaviours all have obvious evolutionary pressures for social species.
No, they don't.
Yes
The primordial matter didn't "come from" anywhere. The total amount of mass-energy in the universe has always been the same. There was never a time when it wasn't what it is.
I like your "You can't explain this except that you can, therefore God" approach.