I do not have a Mac and am writing from my experiences with the Windows version. That version is similar, but the two are not the same. While I used Word on a Mac, that was a long time ago. I am a lawyer. Nevertheless, I hope that I can be of some help.

Automatic numbering, in every version of Word, is best handled using the steps shown in the following page. How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly

The controls on the Mac may be a bit different, but the basic steps are the same. The document structure is the same.

You should adjust the spacing after the number in the numbering dialog while you are setting up the numbering. You should adjust your tab settings in the style definitions but this is separate from the set up of the numbering.

Setting up your numbering using any method other than that specified, with your requirements, will eat up not hours but months of your time if you last that long.

How to attach a screenshot or file in this forum.

A good grasp of Styles is vital. Understanding Styles in Microsoft Word