Just to be clear: I don't charge for this feature.
It's a free offering in Shipnix for everyone who is registered, and then you are free to create servers with this image through the DigitalOcean dashboard if that's what you prefer.
When a new NixOs release is ready, you can log into the Shipnix dashboard, and replace the image with the current stable one, also at no charge.
Not out of the box, although you can upload a custom image to a Space, or you can instantiate a machine as any other Linux distribution and then assimilate it with nixos-infect or similar.
Does this not cover it?