You can use Page Relocator utility of ACS commons for this bulk copy task. For more details please see - https://adobe-consulting-services.github.io/acs-aem-commons/features/mcp/subpages/tools.html 

Adobe uses Fastly CDN and it comes with DDOS protection.  AEM as a Cloud Service also offers reliable protection against (distributed) denial-ofservice (DDoS) attacks on three different levels:• Edge filtering all non-HTTP/HTTPS traffic to block disruptive Layer 3 and Layer 4attacks• Protection agai...

Adobe uses Fastly CDN with AEM as a Cloud service. You also have an option to use your own CDN if you already have one. In case you prefer to use your own CDN then the requests are just passed through Fastly without Fastly doing anything with your request, 

If you plan to use MSM (Multi Site Manager) feature then there are certain best practices which you should follow while designing your content hierarchy. You can find those best practices here- https://experienceleague.adobe.com/docs/experience-manager-65/administering/introduction/msm.html?lang=en#...

You can check the segments API  definition here - https://bank.demdex.com/portal/swagger/index.html#/Segments%20API  You can get the total segment size and size in last 7, 30 and 60 days. 

Yes the foundation components are deprecated. But since there is no alternate yet available in core components, you can create your own version of reference component. It should be easy to build and it will be good if you can contribute it to core components project as well.

I recommend you to pass the JSON object in request body not in query params. And use POST method for these type of requests. 

You will be using AEM in headless pattern in your application. It is a SPA which will own the rendering of components on the page. AEM will provide the content to the app in JSON format. Few things you should consider- 1. What kind of authoring experience you would like ? Do you want authors should ...

Have you configured the dispatcher rules appropriately to not to cache anything under /apps and /libs?  It could be possible the usage.json mentioned in your screenshot is getting cached. If it is getting cached then make sure have disallowed /libs and /apps from the cache in your author dispatcher ...

You can write a request filter to validate the asset before it gets uploaded in AEM.  You can find a sample of that filter here - http://experience-aem.blogspot.com/2018/11/aem-6420-file-decode-filter-virus-scan-to-decode-uploaded-files-for-create-asset-servlet.html