If you want customers to accept a privacy statement you don't need to code.
You can simply go to Admin > SysConfig > Framework > Frontend::Customer and activate the CustomerPanelPreApplicationModule###CustomerAccept
module, and the InfoKey and InfoFile values. When the customer logs in the text in the InfoFile is displayed and the customer needs to accept this. After accepting the InfoKey is stored in the User Preferences. This way the system will not bother asking permission to the customer again, and if you might change the policy you can change the key as well, displaying the message when needed.
For your questions on .dtl files: these are plain HTML files, but different blocks are rendered by the files located under Kernel/Modules.
If you want to modify the page that is used for submitting new tickets, it's this file: CustomerTicketMessage.dtl. You can edit these files with any text editor.