Importing directly from square is a great way to get all your transactions as well as your products and services without having to enter them again. I'd be happy to go over what happens to your current product and services items when you import from square.
When you import your product and services list it won't overwrite any of your previous information in your QuickBooks Online account. In fact it will just create all the imported information as new items unless you map them to the current items you use during the import. I recommend going over this article on how to import and set up your connection with Square.
If you have any questions let us know and we'd be happy to help.