Find and get boundary for admin_level=4 territory

To reply to point 1:

If you want all of them you can use sophox with the following query:

SELECT ?bound ?name ?wikidata WHERE {
  ?bound osmt:admin_level "4" .
  ?bound osmt:type "boundary" .
  ?bound osmt:name ?name .
  ?bound osmt:wikidata ?wikidata
}

Try it

Or with overpass if you want a bounding box selection with the query:

[out:json][timeout:25];
// gather results
(
  relation[admin_level=4]({{bbox}});
);
// print results
out body;
>;
out skel qt;

Try it

With overpass you can download the result of the query in different formats using the button "Export" which maybe replies to point 2.