Causal system, order of numerator and denominator
When $H(z)$ is rational, then the system is causal if and only if its ROC is the exterior of a circle outside the out-most pole, and the order of numerator is no greater than the order of the denominator.

A causal LTI system with a rational transfer function $H(z)$ is stable if and only if all poles of $H(z)$ are inside the unit circle of the z-plane, i.e., the magnitudes of all poles are smaller than 1.

so you also need to find the R.O.C.