Full width scan is the menu you want for the printer to only move the head as far as it needs to to print the smaller images. 'FULL' is the full width of the machine, 'SHEET' will move the head as wide as whatever media is loaded, regardless of what size image youre printing, and 'OFF' will only move the head as far as it needs to print the image. HOWEVER, on a new machine under warranty, if you turn the setting to OFF, and you have issues with the motors, or belts or gears, Roland will not cover those parts under warranty. Turning it off causes extreme wear on the motor and gears, especially if you print small images a lot.
No, VW will never show you the registration marks in the preview.
Either use a rich black, (30,20,20,100) or design in RGB and use a black with 0,0,0 settings and it will be nice and dark. Otherwise the Roland color library black BK21 oe BK22 gives the best results.