reviving 1980 kz1000

I bought a kz1000 a few years ago with 12000 miles on it but it was in quite poor condition. I'm to the point where I need to worry about controls. I'm buying a new master cylinder for the front brakes and rebuilding the rear brakes, but the clutch is quite difficult. I'm not sure if it's because it hasn't been ridden in many years, if the clutch was naturally heavy, or if I have an issue. I actually have an issue pulling the clutch lever back. Where should I start with diagnosing this as this is my first project bike? Do I need to get it started first? replace the lever? replace the cable? replace the clutch?

I would start by looking under the cover where the clutch cable ends. There is a mechanism there where is pushes the clutch rod. Within in that mechanism is ball bearings which may need to be greased. Make sure that moves freely.

Would start by lubing the clutch cable with penetrating oil. If the thing sat for an extended period
the cable probably seized.

I got a similar bike and the clutch plates were stuck together. Sometimes just riding will break them loose but sometimes you have to separate them.

AS others have said, try lots of penetrating oil on the clutch cable and all related linkage - hope your restoration effort comes out as well as mine did on my '83 KZ1100LTD: