I am using Localhost to create a WP site and the files are located at Downloads/users/my-name/sites/
Is this the usual storeage address?
It doesn’t matter where you store your files… from WordPress’s perspective.
The ONLY thing that matters is that you configure your webserver to point to that location as the DocumentRoot for the site (and it doesn’t matter whether it’s a WordPress site or a static HTML site).
Is this address OK to FTP upload from?
I’m not sure what you mean. You said your site is on localhost
(ie on your personal computer, not on a remote hosting server), so what are you FTPing to/from? What exactly are you trying to accomplish with this?