If you are sizing a transformer for a fire pump, that would appear to be a minimum requirement. Section 695 deals with fire pumps.
Correct. However, the NEC is primarily concerned with safety, and sets forth minimums to establish reasonable safety. However, conformance with these minimums does NOT guarantee that the system will function acceptably.
Again, safety in the case of a fire pump generally means running the motor to destruction, if necessary. Not much sense in shutting down the motor if the building is still ablaze. Saving the motor and sacrificing the building is poor economy.
This is an engineering issue, rather than a code issue. It really depends on how much voltage drop you are willing to tolerate during the starting period.
In very round numbers, in the case of a transformer feeding a single motor load, the voltage drop ( in percent) will be equal to the transformer impedance multiplied by the percentage of transformer full-load rating drawn during the starting period. There are many assumptions built in to this statement, but these assumptions are usually valid enough.
For example, let's take a transformer of 5% impedance with rated secondary current of 100A. If you connect this to a motor which draws 600 LRA it is reasonable to assume (to a first approximation) that the transformer secondary voltage will drop 30% during the starting period. At first glance this looks like a problem, but as far as the motor is concerned it probably doesn't matter as long as you have enough starting torque at the reduced voltage. Remember that reduced voltage starting techniques routinely start motors on 50 percent voltage and even less. The transformer won't care as long as the starting period is only a few seconds.
The problem you may encounter is that control devices; relays, contactors, etc. tied to the secondary of the transformer may not work properly under the low voltage conditions. If this is the case it is probably most economical to run the controls from a separate transformer so that they are not exposed to the low voltage during the starting period.
If your transformer is feeding only a single motor, and you can tolerate the reduced starting torque, you calculations should be OK.