Not really. In theory you could decide that the doc list is your highest level, and create multiple docs within it. But I think the best UX is as you were already describing: create a company wiki/knowledgebase Coda doc, with pages and subpages inside it for the content.
If you’re only going to be using Coda for a single wiki doc, and truly never anything else, it’s probably not the best solution (consider Notion, Slite…).
However, I think you’ll find many use case for Coda beyond wiki (my company has dumped at least 4 other SaaS subscriptions after being able to replicate and improve upon the functionality in Coda). With this in mind, I think you’ll appreciate later the ability to have multiple separate docs (which can be, as Coda claims, “as powerful as apps”), outside of what’s in your wiki.
One other thing to note is that if you have certain content that only certain groups or individuals should have access to (not everyone in the company), then you need to create a separate doc for each of these information sets.
You can’t manage permissions for pages and subpages within a doc currently.