You don't have to link Heading 6 to level 1, Heading 7 to level 2, etc.
You can leave them at their own levels.

The idea is that Headings 6 - 9 will provide an outline in and of
themselves - one that starts with the first appearance of Heading 6.
Since no level lower than 6 will appear for the rest of the document,
Heading 6 will restart the other levels (and itself) as if it were
Heading 1.

You don't have to base your Heading 1-9 styles on other Heading styles,
either.  They can be based on Normal; in that case each will be
independent of one another except for the numbering function.

There are two big advantages to continuing with the Heading styles for
the second outline: (1) You can automatically insert the Appendix
numbers into the page numbers if necessary and (2) you don't have to go
to the trouble of creating an extra list template with extra styles.

You didn't have to name the list template, although it certainly
doesn't hurt and could possibly help if you get involved with VBA.

The key to setting up the Heading styles is to link each properly to
its appropriate level.  From there on in it's all grunt work.

When you go into Format | Bullets and Numbering through the Level 1 style,
you can format any of the levels in the outline and link it to the
appropriate style; you take care of the formatting for all the levels in a
single pass.

But from your description it would appear that G. G. Yagoda is correct, and
that what Shauna is suggesting here is a new, separate outline-numbered
list. In that case, your Level 1 style is Heading 6, so you always format
the numbering of that list by going in through Heading 6.