Is it possible to build content for MonoGame 3.0 without having to install Visual Studio 2010 and XNA 4.0?
The content I have to build is:
I am aware that there exists MGCB, but before I try and use it I need to know if it is reasonably reliable for what I need it to do.
I'm no expert in this area, but I noticed you don't have an answer yet so I'll try my best.
Having Visual Studio and XNA Game Studio 4.0 installed will allow you to create Content projects that can compile your content into XNB files. Those XNB files can be used in your game without Visual Studio. You can use Xamarin Studio instead.
However, it's also possible to use some content directly. For example, you can use raw PNG files instead of compiled textures and you can build your own system for fonts. I'm not sure about 3D models.
I can't vouch for MGCB but I've read that the MonoGame team are currently developing the content pipeline. If it's not working now it probably will be in the not so distant future.
So yes, it's probably possible.