Hi,
To create a glow layer map - just use a version of your top diffuse full texture map. Then make black the colour of the elements that you don't want to glow. Make the elements to glow white or degrees of grey to white, depending on intensity. But I've just usually just used a black and white map, the subtlety of degrees of grey don't really make a difference unless your camera is really close to the object.
For the compositing, I'd render once for diffuse with all textures and objects active/ on. Then in the second render turn off/ hide all non-glowing objects, turn off all lights, turn off diffuse textures and just keep active the glow map on objects. Essentialy the render will be all black and only the glowing areas will appear. Then just composite both renders in AE or similar program.
Hope the above helps.