Hi Jenn
Your Davis was made in 1917 and uses a standard 15x1 needle. Belts and bobbins can be found on ebay or someone that deals with vintage/ antique parts and supply. You can get a manual copy from the Davis VF group:
http://groups.yahoo.com/group/davis_vf/
Good tutorials on the QB for cleaning and oiling and is also in manual (oiling). Don't remove faceplate unless your comfortable doing it as it's more complicated than the usual SM. You got a great deal and a great sewing machine. Good Luck
Jon