Freezing Touch is an impactful spell, approximately 1.5 times weaker than Earth Shock. The advantage of Freezing Touch over Earth Shock is that it can reduce the enemy's initiative with the appropriate skill (0.3 turns), and moreover, the damage dealt to that creature will sharply increase during one turn (by one and a half times – easily, it can even be doubled). Therefore, a stack under Freezing Touch can already be automatically considered as a corpse.
Regarding the fifth level of the Tower, it depends on you. Of course, some Kaspar might appear early, but that means you need to try to avoid such a possibility. Usually, the fifth level is built without any particular problems.