Unfortunately, at this time, there is no way to lock annotations made by other users.

No. You can only delete and recreate. Subdomains should work though. Be sure to add something likeadobe.comnot*.adobe.comor.adobe.com 

Domains or subdomains? If it's subdomains, you can create creds for just yourorg.com and use the same creds across all subdomains.

That's currently not possible using just Embed API. However, It would be easy enough to integrate our PDF Services API to "split" the PDF file and retrieve only the pages requested and return that to the browser. 

Are you asking if only one page of a multi-page PDF can be downloaded to the local device or if the viewer will byte-serve the PDF a page at a time and start to show it before the full file is downloaded?

I haven't seen the roadmap but to the best of my knowledge, we're targeting PDF 2.0 with Embed API and I suspect you know what that implies. Also, I don't recognize your screen name or I'd have said "Hi" too.

Dynamic XFA forms are not supported and only the AcroForm fallback is supported for Static XFA. At this time, no JavaScript or FormCalc is supported and no field properties are supported.

Does that site actually exist?