Instead of Type 1 Engine and Type 2 Engine that really doesn't differ from each other, make a standard Engine and a Rescue Engine. The Rescue Engine of course would cost more than a standard Engine, but could double as a rescue. The Rescue Engine could speed up the completion of "rescue" type calls and a standard engine could speed up the completion of "fire" type calls.
Also make it where you do not have to have a specific number of engines but maybe a specific number of personnel on a scene. Where I am from it is nothing to have only one or two engines operating at a call, but several other apparatus bringing personnel in to the scene. I can see the required amount of rescues or ladders however.