1. I usually do painting through the following method: a. Make sure I'm in the Blender Render mode. b. Use the Texture Paint Layer Manager. (Hit N in the 3d view to see the layer manager.) c. Be in GLSL shading mode. This allows you to use the shader properties to get your shading information. So, you can set up lights how…
Hmm... If you show me the functionality you want, I can see if I can either find the right tool for you or script one. The merge to center with limits sounds like it is fairly trivial, so I can try tackling that.