If you have multiple sites on your server and wants them all to only have a document library overriding presets.xml is absolutely the way to go. If you just have one site on your server you can of course simply use the "Customise Site" page found under the "More" menu (in your sites title bar) and simply remove the pages you don't want from there.
When it comes to "how to remove the Site Dashboard and the Site-Members field?" there is unfortunately no way to configure this so you will have to override the collaboration navigation component's html template. To do that you have to: 1. Create the following directory structure on your server: "<SHARE-TOMCAT-INSTALLATION>/shared/classes/alfresco/web-extension/site-webscripts/org/alfresco/components/navigation/" 2. Copy the file "<SHARE-TOMCAT-INSTALLATION>/webapps/share/WEB-INF/classes/alfresco/site-webscripts/org/alfresco/components/navigation/collaboration-navigation.get.html.ftl" to your new directory. 3. Modify the file and remove the links to the dashboard and and the site members. 4. Restart your server. (This will of course affect all the sites on your server.)