I would first add a form button on your item detail page. Use the form button to write a unique value from the Item details (using Column Value components), your note (using a Note or other entry component), the reminder date (using a date entry component), and user email if needed (using the Special Values components).
Next create a relation column to link the unique value from the Item sheet to the identical unique value in the Notes sheet. You will use this relation to create an inline list on the item details to show each note.
Your Today reminder tab could either be the Notes sheet, or another sheet where you add an inline list pointed to the notes sheet. You will then filter the inline list where the date that was entered is within Today.