It is not clear to me what you're asking outside of "How do I import files", but I think you know the answer to that.
Your tagging is lost of course when you delete files if metadata was not written out to the files. Many tags are not written to image files (keywords are by default).
When you permanently delete items from MC's library, the metadata goes with it to the digital black hole.
When you soft delete, you're removing items from MC's library, but references are maintained in a generally hidden database called the Removed database. This is so MC can avoid re-importing those, and so that you can quickly move those entries back into your main database with metadata should you decide to re-import them.
You can clear out entries from the removed database manually if you want. Or you can manually import files to override the auto-import's Don't reimport files already deleted setting.