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.

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.