Clarification: Mass Action -> Export | Editing CSV file | Import

Hi,

Go in the menu Products->Products, select on the left explorer the category you want to export, set the dropdown on the top right to "all sub elements" and finally click on the "export" button at the top. That will export all the products of that category in a CSV file and you'll receive automatically.

Excel should be fine. However, I would recommend to use instead LibreOffice. It works much better with CSV files, and it's totally free.

And no, you don't need a product template. A product template is useful when you're importing new products that will all be setup in a similar way and you don't want to provide everything in the CSV but let the system generate the products with the imported data and for the rest of the data get it from a "template" product.
For example, if you're selling files when many settings all similar but only the name of the product and the file name being different, a product template is a good way to import all your files at once with a CSV with the name and file name of each file and the rest being automatically filled in based on one product you already precreated.

Yes, you should not import products with the same product_id of products already in the database or you'll loose the ones already in the database. The goal is that this allows you to update products already in the database.