First step if you're hosting it at home is separating your home connection from your business connection, physically. If you don't have that, do at least two VLANs.

Second step, don't expose anything unless you explicitly know what it's for. Start with everything 100% locked down, and only open things up you know want to be open. If you're just hosting a "home" cloud, nothing have to be exposed externally, so expose nothing. Otherwise go service/port by service/port to expose things.

The Kubernetes nodes and control plane are not something I manage directly. DigitalOcean perform regular upgrades to keep the cluster at a minimum supportable and secure version. They're reasonably sophisticated, and if they can't upgrade the cluster without downtime they'll notify you with what's wrong - which is great, because I don't know much in depth about K8s administration.

The configuration you use is pretty explicit about which ports are internal and which are published externally as a service, so it's unlikely you'll get it wrong by accident. Nevertheless, you can still verify that you haven't done anything daft like opened a DB port to the internet by e.g. trying to connect to it.

Finally, there's a whole class of difficult administration, hardening and access problems that can come with Kubernetes multi-tenanted operations that you just side-step as a sole administrator/user. You don't need to worry about who has access to which services or namespaces, or what privileges they have via RBAC - it's just you. I'd want to do some really serious research before letting other users launch containers on my cluster, or execute their own code in it; but that's not one of my use-cases, so it's not a problem.