what actually is orchestration?

We do some very basic automated pull-request testing that mostly amounts to installing the whole environment on minikube inside CI and making sure everything installs and there are no syntax errors. Ideally we would then run some end-to-end tests on that environment; right now, we don't, and instead rely on a cloud-based integration cluster and automated integration testing.

Mostly for development beyond the basic unit test sort of stuff we use a dev cluster in the cloud (on Google Kubernetes Engine to be precise). It's just easier and less fiddly than a local install, and GKE is rock-solid. That of course comes with a monetary cost, although IMO it's pretty small compared to the cost of developers. But not being able to test locally easily is a bit of a gap that does occasionally cause problems, and while minikube is in theory an answer to this, in practice it's tricky to get all the pieces working happily on a laptop for typical local development (particularly on modern macOS, which a lot of people like to use but which adds the wrinkle of not being x86-based).

In terms of reference material, honestly I mostly just read the Kubernetes reference and tutorial pages on kubernetes.io (and of course implementation-specific guidance for specific cloud providers), plus the Helm documentation. But I joined a team that was already doing Kubernetes, so a lot of my training was from watching what other people were doing and asking questions, so I'm maybe not the best person to ask about initial reference material.

We use Argo CD to automate our Kubernetes deployment and maintenance, and I cannot recommend it highly enough. It makes it so much easier to automate the deployment process end-to-end and then be able to easily see what the cluster is doing and debug problems (and upgrade things, which is very important since we have a very fast development pace and are usually updating five or more times a week). I'll fall back on kubectl for some specific problems, but the Argo CD interface is usually more useful, and I say this as someone who almost always prefers command lines to any graphical tools.