>> 1. A solution for unlimited scheduled snapshots without affecting performance.
You can very comfortably have instant and virtually unlimited snapshots with zfs/jails (only occupying space when files change). Very easy to automate with cron and a shellscript.
>> 2. API access for managing configuration, version updates/rollbacks, and ACL.
>> 3. Close to immediate replacement of identical setup within seconds of failure.
There is a lot of choices for configuration management (saltstack, chef, ansible, ..). I run a shellscript in a cron job that takes temporary snapshots of the jail's filesystem, copies to a directory, and makes an off-site backup. A rollback is as simple as stopping the server, renaming a directory, and restarting it. It's probably more than a couple of seconds, but not by much. I think I'm uncomfortable exposing an API with root access to my systems to the internet, but I'm not sure how these systems work. I don't think it would be hard to set it up with flask if you wanted it though.
>> 4. No underlying OS management.
I don't know what this is, but I'm curious and looking it up :D.
In most of the posts I'm reading here, people have really beefy rigs. But you could do this on the cheap with a 2000s era laptop if you wanted (that was my first server).