Yes Content Repository and crx-repository are same. If you intend to use only "Document Security" module, then you do not require aem-forms-add-on package and Content Repository. See the LiveCycle ES4 SP1 > AEM 6.4 Forms on JEE section in the following article for detailed upgrade instructions:
Adobe Experience Manager Help | Upgrade to AEM 6.4 Forms
Install and configure Content Repository only if you plan to use following capabilities inAEM Forms on JEE:
- Adaptive Forms, Correspondence Management, HTML5 Forms (Known as Mobile Forms in LiveCycle ES4 SP1), Forms Portal, HTML Workspace, Process Reporting, Forms centric workflows on OSGi,
Depending on the module being updated, the updates are still available as .exe files and .zip (OSGi) bundles. For the list of available AEM 6.4 fixes, see AEM 6.4.1.0 Release Notes