for the second question ,you can export the CAM files using export button in CAM window and then you can reimport it back in your new design
3) It looks like the defaults are still set from very early versions of PADS (old school). I work with some very experienced designers who put lots on the top layer and then separate it out in the Gerber file creation. Personally I prefer to separate it early in the design instead of later in the Gerber file generation. Thus I use my own settings, not the defaults.
2). What SK said. <File><Cam><Export>