seems like it's nearly working. my tomcat-users.xml has the entries already, apparently imported when I created the server in eclipse. did you restartet the server after editing?
found a solution. the problem is like I said the webapps-folder within the workspace and the missing manager app. you need to add the folowing line to the server.xml in your workspaces server/tomcat folder
Don't know if you kept in mind that from within eclipse the webapps gets deployed temporarily inside the workspace, for me it's .metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps
works for me, but are you sure about the port 80 in tomcat.manager.url in the build.properties because default it's 8080, unless you changed it in tomcat's server.xml