Four towers would be great, one in each quarter.
Anywhere you go, these articulating towers are incredibly expensive. The up front cost is in the millions, then the training, the regular maintenance and so on. This is why Montreal runs a pair of T-Rex units in front line and two as spares. Toronto Fire also has two (not including Tower 1) bronto’s in front line service and two spares. Other than the “up and over” reach, many cities get by fine with buckets on sticks. FDNY has had great success with there fleet of aerialscopes. Personally, I wish CFD had ordered mid mounts platforms, but that’s only because I think they look cool.
I can see Tech Rescue 11 replacing the support unit at 10. The tandem rescue is a really nice rig with tons of storage.