- A reference guide and manual in Russian for Heroes 3.

In other words, does it even matter if there's one Cyclops King or 1000?

Exactly... The number of Cyclops in your stack doesn't matter for the enemy's fortifications.

And also: what is the chance of a ballista hitting the point of impact of a catapult's attack? (i.e., if I aim at the central gate, what is the percentage chance of hitting it?) And does the percentage differ between the castle walls and the arrow towers?

Don't think I'm being rude... but you really can't find time to read up on physics, can you? :)
Sheet #29. City fortifications and their siege. In particular, point 4 "Catapult and calculation of its effectiveness during a siege." It's not entirely straightforward and there's room for debate, but it provides enough basic information. We don't need to include tables with probabilities here...