So essentially what setup does is run you through creating
package.json, and sets up the database.
So after running setup once, you can just copy those around between everything else, adjusting the address of the database and whatnot, and running
npm install to install the deps, or just copying the node_modules directory for that.
Also you'll probably want to set a custom uploads folder.
Nginx site name should be whatever your load balancer is passing through, which should usually be your site address. If you're using a load balancer already, though, you probably don't need nginx in between. the nodebb url should be the URL that you see in your browser when you visit the forum. (for instance, it's set to