You’ll have a hard time finding much specific info on this, because, frankly, what would you even search for?
MongoDB is a proven system, so it handles many kinds of common workloads without an issue, and so noone would be writing about that on the internet. And noone will, or can, tell you what exactly the resouce requirements will be for your specific app/service.
Just get started and keep an eye on things, and if you encounter specific issues then you’re likely to find answers. And if you see your app growing beyond the resource constraints you have set you of course either optimize or increase resource allocation, or a mix of both.
What you feel is probably mostly the uncertainty and slight discomfort of doing something for the first time – deploying a production app, in this case. No cure for that but actually doing it, moving ahead, experiencing it. At least that’s the vibe I’m getting from what you’re sharing (And absolutely nothing wrong with that, of course!)