Hello! We used two of the thin motors to minimize weight of the Z carriage and to allow for a larger range of Z motion. You could certainly try with just one of the thin motors for the 'Y' axis (bottom one), but you might need to have an elevated build surface as compared to the mounting base of the printer arm to make sure that the print-head can reach the build area. I don't think there would be any weight issues caused by the larger motor, but it is a possibility.
I wish you the best of luck with making your printer, please share pictures and provide feedback when you're done!