"Catalogue Contents" Panel when Importing from another catalogue is too small and not very useful.

I wold probably use a different method to achieve selective transfer of photos between Catalogs. That would be, to first highlight in the 'donor' catalog all the photos concerned, selecting them by whatever means. Then use Export as Catalog (to a new temporary intermediate Catalog) including only these highlighted images. This leaves the same images still highlighted inside the 'donor' catalog in case you wanted to bulk remove them, or otherwise mark them with a keyword, as part of your process. Then the new intermediate Catalog can be entirely merged into the 'recipient' Catalog using Import from Another Catalog. Being pre-filtered, this merge will not need any selectivity. Then the intermediate Catalog can be deleted.