Aribeth, you can pretty much do all the things; but it would be difficult to answer all your questions comprehensively at once, even if I could

So, I'll say this: you aren't wandering in the woods with your observations and questions, in fact you're pretty much right on 'the path'. You are correct that blender models and rigs will be of great use; that said, you dont /have/ to use blender, just about any capable digital 3D design tool will do. Of course, proficiency with tools like photoshop or the Gimp do not go wasted either.

The thing to know about doing content work in SineSpace vs. doing it in Unity3D, is that SineSpace is a set of Unity Editor Extensions, and there is a client enabling a security model and realtime experience sharing (and a bit of managerial service structure on the backend). Really, when you do SineSpace content, you're doing Unity3D content, up to a point.

Perhaps the greatest difference is that unless you have (a) white label region(s), any coding you do will be in Lua, instead of c#.

My advice: keep on doing what you're doing! Make stuff with blender, even if you cant put it straight to use. The models will then be there when you are ready. In the meantime, keep asking questions and filling in the blanks in your knowledge and understanding.

You will progress

Cheers and welcome to the fun!