I think the current hardware for Lemmy.world should handle maybe 1M users, if the Lemmy software is tuned.
If it should grow more, we need to look into horizontal scaling with Kubernetes.
But hopefully there will be more and more servers so the users can be spread more.
Thanks for hosting Lemmy.world! Does Lemmy use a database? Until the software gets horizontal scaling capability, could we use a central RDS so the load isn't on the EC2 instance's CPU? Then we can use load balancing between multiple instances that pull from the same DB? Obviously, the db instance is still a limiting factor.
How are you paying for this? Is lemmy.world controlled by you as a private individual? Is this going to be transferred to some sort of non-profit, or business entity? What are the options where you are at? Have you considered the legal aspects of various locations, (e.g. free speech protections, reach of law enforcement, etc)? Since this has the potential to blow up, now is the time to start thinking about these things?
Sorry if you already know this, but this might be helpful for lurkers that don't know such a thing exists.
I don't know anything about dutch corporate structures, but some US states have an entity called a benefit corporation. Think of it like a non-profit and corporation hybrid. It allows you to make a profit and grow, but operate like a non-profit where the purpose of the organization is something else. This gives you more flexibility that might not be available as a non-profit. I believe you can even incorporate as a non-citizen (I'm assuming here). Might I suggest an ask lemmy post to get ideas?