Experienced builders, almost without exception will tell you to not install the small spring. There is no need for it. The internal clutch return spring is quite strong and it will suffice to completely engage the clutch pads and pressure plate. As for lever return there's no need for that either. When the clutch is engaged, handle not squeezed the cable, if adjusted correctly, will be pulled tight anyway. It doesn't need a spring to help it return.
You don't need any special 'cable lube'. Any light oil will work just fine. I don't like grease and prefer something like 10w or 20W oil instead. That assures the entire cable and the housing is lubricated where grease might not reach every surface. I typically re-lube the cables semi-annually. You might get conflicting advice on that but I'm just passing along what works well for me.
Tom