Primary question:

NPR is very slow, beautiful but slow. A) I would be inclined to build some watercolor shaders and then experiment with color clipping, or B) Another way might be to use a uniform white shader on everthing but create watercolor gels and project onto the objects. Since you can deselect object from being lit by any individual light, you could pretty easily control the effects placement. 

Other questions: 

1. Set up your scene and utilize a speherical camera for a scene render, placed at the center of the scene. As for HDRI application, check out this tutorial I made few years ago.

2. Vector paths do not import into the Vertex room. You can bring them into the Spline room, create a shape and then convert to polygons.