Without a video card in your computer, you wouldn’t be able to see anything on your computer. I don’t think most computers will even work without some sort of video card installed. A video card offers several features. The most basic and important benefit is that you can plug an external monitor into it to see what you’re doing. Because working with Cubase requires working with many windows open at once, I highly recommend a video card that will support at least two monitors.
Single- or dual-monitor setup? If time is valuable to you, spend a little extra and get a dual-monitor setup. If I could have a four-monitor setup, I would. The extra monitor helps save so more time when you’re in the studio.