Automated Testing Framework
One of the first things coming to mind when I think about systems modelling and simulation is automated testing. Unit and integration tests are probably the most efficient way to assert that specific desirable behaviours remain the same during extension of the simulation model.
What plans do you have in that direction? Have you already settled on a specific test framework? The only somewhat promising, free one integrated into Unity that I could find was the one from Unity Technologies themselves:
I usually try to implement my code according to <a href="https://en.wikipedia.org/wiki/Test-driven_development">TDD</a> and therefore have quite some experience with automated testing in general, as well as with architectural tricks to make 'legacy' code unit/integration testable - if I can help in any way let me know. :)
Because the client is little more than a "player", the whole simulation (and most, if not all logic) is done server sided, whatever works on .NET is usable. So basically, we're not restricted on stuff that works with Unity or on Unity's old Mono.
That means that if there's a need to have unit tests in the client though, those need to be separate - which is probably a good idea anyway.