One of the first uses I made with Calibre was to document my 40 Year Paperback collection.
Create
Empty Books
Add :from ISBN for all that had those.
IF they had (978 series) Barcodes, I used a Keyboard Wedge scanner (it emulates Key presses)
OR
If you have a spreadsheet /text list, you can paste a bunch instead.
Do small batches (10-20) so you can easily resolve 'not founds'
The rest (problems or no ISBN), you keyboard
As to tracking Borrowed: Create a Tag-like column and manually log the name/ID
You can search for an ISBN (or other ID), just include the type : and the ID value
eg