I would start by flushing the fluid in the clutch system first to see if that helps the creeping at a light. Brake fluid is cheap. If that does not fix it then you will have to do the rebuilds / replace master and slave.
It is usually better to replace the slave with a new slave rather than rebuild. The issue in the slave is usually corrosion and the rebuild kit will not fix that, and the rebuild kit is not much le$$ than a new slave.
There is a good chance that your clutch is fine, the stock spring is known to die of old age and the first symptom is slipping when you get on the throttle. You will not know if you need new clutch plates until you take it apart and measure them. New plates are 3mm (0.1181 inch) thick and worn out is 2.8mm (0.1102 inch) thick.
Skydoc_17 sells a spring kit with a slightly stronger spring that will not slip. If you need them he also has the plates.