Solution to keep complete projects completely separate with same user and multiple displays on macOS? I'm trying to figure out a simple way one can work on multiple complex projects simultaneously and switch between them elegantly and quickly, without the need to close down applications from one project to work on another, or thoughtfully organise applications and windows beyond simply grouping them by project.
I assume a typical setup that this applies to has:

multiple displays (say, 3)
~10 applications open per project (that is, they're real, complex projects)

What I am trying to achieve is a way to switch between projects seamlessly and keep windows and instances of applications grouped together.
Example
Project 1: rails app

Display 1: browser windows
Display 2: Multiple instances of sublime text for code editing
Display 3: terminal (multiple instances)

Project 2: machine learning in R

Display 1: RStudio (4 instances)
Display 2: 3 x Browser (multiple tabs in each)
Display 3: terminal (multiple windows)

There could easily be one or more additional projects.
Partial Solutions

I have tried using different user logins to the MacBook. This works somewhat but is very clunky and slow to switch between environments
Using multiple desktops - this sounds like it would solve this problem but it requires management of desktops across each display. So, for example, just 2 projects on a setup with 3 displays would mean managing 6 separate desktops (and good luck if you have &gt; 3 displays and &gt; 2 projects to work on - very messy)

Desired result
Some way to easily switch between the collections of contents across all displays quickly and easily, preferably via a touchpad gesture, keyboard shortcut, or clicking somewhere convenient (but open to less ideal triggers). I have a preference for something build in to macOS (hacky or otherwise), but am open to other software too
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 ^^