Yes, that is one possibility. Another is to embed Rhino inside an existing application.
No, Rhino would still need to be installed on your computer. For accessing Rhino functionality without Rhino installed, you would need to use compute.rhino3d.com
We don’t know yet. Our development process is “throw it over the wall” and let customers tell us what they need.
Yes, only .NET (at least for now). That doesn’t stop you from hosting .NET in your own native application which is exactly what Rhino.exe does