You're seemingly headed for what is known as mandatory access controls with compartmentation; a trusted execution environment. Mandatory controls do get expensive to build and operate, and mandatory controls are gnarly to manage, too. And macOS doesn't particularly support mandatory controls for user apps, and particularly not after Xcode 9 and macOS High Sierra and TrustedBSD.
The usual response to these requirements is multiple "system high" Macs, or maybe multiple guests in a VM if your local security policy allows that. Which also gets expensive, but less so. All as you seem to be aware.
If you really need this isolation for your apps, then SELinux might interest.
Intel tried providing something similar to your requirements with SGX, but has seemingly largely given up on this outside of servers. Apple doesn't offer anything similar to third-party developers.
PS: For low-level information on macOS, the set of books comprising the New OSX Book might interest.
PPS: You'll likely need to discuss these requirements with the folks managing the content filter and endpoint security on this Mac.