Solution to keep complete projects completely separate with same user and multiple displays on macOS?
If Apple’s native Mission Control doesn’t give you enough functionality, I can only suggest exploring professional apps.
Have a look at Workspaces. It groups your apps, folders, website links by project, is that close to what you’re looking for? Maybe you could use a combination of Workspaces (for grouping and easy access from Toolbar) and Mission Control (to separate into individual spaces)?
Workspaces is also also available to download through Setapp, which gives you access to multiple professional apps (it’s like Spotify of apps). I use it myself, sign up using my friends link and we both will get a free month! :)
On a personal note, I’m barely able to keep two apps open simultaneously (4GB CPU), so I’m slightly jealous of your situation ^^