I use copper pours for my GND and Power plane layers, so I have 'Routing/Split Plane' selected. The help button describes the different document types:
- Custom— Create your own definition for a document. Use the Select Items Dialog Box to specify which objects appear in the document.
- Routing/Split Plane— Document layers that contain plane areas and/or routing. Use this type for Split/Mixed and No Plane layers. Conductive elements appear black in the CAM Preview window.
So 'Routing/Split Plane' is easier to use; you have more control with 'Custom'.
I always use an external Gerber viewer (I prefer ViewMate, others like GCPrevue) to make sure my Gerber files are what I want. You can play around with the different options for the layers and see what looks best.
About the warning, check your drill table in your drill drawing Gerber file. You'll see '+P' symbols. These are acceptable but if you prefer something else, go to <File><CAM>(select your drill drawing)<Edit><Options><Drill Symbols...> and then hit <Augment> to add symbols or <Regenerate> to rework all the symbols.
Thank you very much for the clarification!!