Most people base their styles on the normal style. Most styles that are built-in with Word are based on the normal style.

I generally base mine on the Body Text style. That is more habit than necessarily good practice. There was a time when basing on the normal style was not a good idea. I do not believe that is still the situation.

OTOH, by basing on the Body Text style, which I base on no style, I have more options.

What is the difference between the normal style and the Body Text style?, by Suzanne Barnhill, MVP

The heading styles are special. Many, but not all, of their special characteristics carry through into styles based on them.
Why use Microsoft Word’s built-in heading styles? by Shauna Kelly

Much more important is I never leave a document with the setting to update styles from the template upon opening.

I generally cascade my heading styles and my body-text styles.

This also ties in with Themes and Style Sets in ways I do not fully understand. The key thing about themes is they will set a font for headings and body which can be carried through in all of your styles if you use them.

Final note: A good understanding of styles and use of styles is essential for a happy use of Word on a regular basis. The program is very heavily based on styles and many of its features are only fully available through using them. See my My test of 100-page document and my remarks just before that for some of my history with styles. Yet Another Verbal Beating About Using Styles by Dian Chapman.