A D1 is a very nice machine. I wish you good luck with it. To check it out, your could spend $$ and bring it to a Viking dealer or I would start on the sewing side with button holes, straight stitch, zigzag etc. Then attach the embroidery unit and stitch out a design. Don't worry about color - just stitch it out. Some Viking Dealers will allow you to "purchase" classes - you could check on that. I am however concerned about the comment that the bobbin "chatters".
SO ... I actually worked for Viking when the update came available to transform the floppy systems of the D1 to USB. My caution here ... if it were mine I would not do it. The USB conversion required (at least back then) that there was a special piece software that had to be on the stick and the time to load a design was much longer than from the floppy. Maybe they have gotten better.... but about 50% of the time you had to reseat the usb stick several times before you could load a design.