Hi,
You probably want to create custom fields of the table "product" and of the type "text". That way, the text that you enter in the custom field in the backend when you edit the product will be displayed automatically on the product page.
If you want to have the custom field itself on the product page and not a value, then you indeed need to create a custom field of the table "item" and this would indeed require the Business edition.
If you already have the Essential edition, you can upgrade by purchasing this product with the same user account you used to purchase the Essential edition:
www.hikashop.com/extensions/upgrade-my-version.html