Multiple references to same note
Insert the first occurrence of note as usual. This creates an internal bookmark.
For the subsequent occurrences, use a cross-reference to this bookmark. At the location of the occurrence:
In Type, select Endnotes or Footnotes; click on the relevant note in Selection; choose Reference in Insert reference to; click
Select the newly inserted reference and give it character style Footnote Anchor or Endnote Anchor so that it has the same formatting as other occurrences.
Title before endnotes
You have two options here.
Since the endnotes are collected in pages with page style Endnotes, you can add a header in this page style and the header is repeated on every page.
If you prefer a single heading before the notes, see Heading for endnotes page in this site.
If this answer helped you, please accept it by clicking the check mark to the left and, karma permitting, upvote it. If this resolves your problem, close the question, that will help other people with the same question.