How to set up a sitemap?

Question

Google

Hello.
There were questions about indexing the site through the sitemap.
If you just specify the main page as mandatory for indexing, will other pages of the site be indexed?
Do you need to edit and update lastmod after every change on the site ?
What's the best way to prioritize?
Is it possible to specify in the sitemap that it is necessary to index sites starting with the address site/papka/... ?

<loc>https://site</loc>
  <lastmod>2018-03-02T23:56:12+00:00</lastmod>
  <changefreq>weekly</changefreq>
  <priority>1.00</priority>

Answer 1

If you just specify the main page as mandatory for indexing, will other pages of the site be indexed?

Will
Possible, but not required
It's better not to put them
This is indicated in robots.txt

Answer 2

1) it will or may not, that is, the indexing of pages not listed in the sitemap is not related to the sitemap in any way.
2) it is obvious that yes
3) prioritize pages that are most interesting to users
4) this is not a robots txt