For scalability, there are many ways to optimize the site.  Here are a few ways:

1. Leverage Adobe Target or AEM personalization for personalized content so most of the page can be cached.
2. Use Sling Dynamic Includes to do ESI calls for caching the user's personalized info. This helps avoid a lot of backend calls while still caching the rest of the AEM page.
3. Leverage Cache-Control header for caching in CDN and browser.
4. Implement the site on the latest AEM version to benefit from performance enhancements to Oak repository and and its User Management.