You are asking many questions with side references but no links or images.  BB has many posts and threads both here and RuntimeDNA.  It would help if you break down your questions to specific categories with images, if possible.  It will help us better to help you.  However, you must become familiar with the many rooms Poser has to offer.  Only the manual can tap into each aspect, providing the information necessary to get you off the ground.  And have you read the manual yet?

Just to answer your first question, no; not everyone use objects to provide environmental light.  We only use them as another enhancement to shed an ambient illumination to a scene.  Don't get me wrong, they are great as a light source also, but a series of different render settings are needed to make them work properly.  

Making an object emit light is just a simple setting in the Advanced Material Room.  On the PoserSurface node, there is an Ambient Color and Ambient Value; driving the Ambient value to 1 or greater will make an object emit light when you render with raytracing and IDL.  If you are not familiar with these terms, again I suggest reading the manual.