For your driver card:
A lot of your questions are specific to the driver card you have. The amount of drive current needed (from a parallel port) is determined by the inputs on the drive card. Some require no buffers, others may not work off the low current lower voltage outputs of recent parallel ports.
Your driver card may have an 'enable' pin that needs a logic signal (high or low?) to let the signals through.
No ground to the motor card = no signal. You have to have a ground return for the logic signals. On some cards/drivers the common is a +5 (supplied externally in most cases) and the step and dir signals are active low, meaning they are the ground return.
Sometimes trying to use poorly documented or poorly supported electronics can end up in a long learning curve that will cause frustration and often stops the project.
Tom Caudle
www.CandCNC.com