Installing folder action workflow on startup

Once a folder action is assigned to a folder and enabled (automatically done by Automator), then that folder action is active across reboots in my experience. RIght-click on your Downloads folder icon and from the contextual Services menu, select Folder Actions Setup… You may be greeted with a dialog confirming you want to run that service and click on Run Service button.

Next, you will be shown a scrollable list of folder actions which you can locate your folder action by name, and once selected, you will see a panel that should show Enable Folder Actions selected, your Downloads folder showing it is On, and the appropriate folder action script in the right-most panel, also On.