I suggest you consider creating a "import repository" Lightroom catalog on a dedicated external drive and import everything to it, then, after deciding on the files you want to keep working on (or after doing some preliminary work there), export them as a catalog to your computer (e.g. to a temporary folder on your desktop).
Then, from your main catalog, import those files using the "import from another catalog" command (moving them, as necessary, to a new permanent location elsewhere on your computer). Once you backup your main catalog and its files, you can delete the temporary folder from the desktop.
I further suggest that you not delete any files. Going back to things months or years later can reveal keepers you didn't recognize as such at the time you originally imported them.
In my workflow, I have an external drive dedicated to making a backup of my import repository as well a two drives for backing up my catalog and files from my laptop each day I work.