Although there is no such thing as an ideal op-amp, you can assume the ideal op-amp early in the design stage.
However, you should consider the differences between the ideal and real op-amps when you proceed to the detailed design stage.
For example, if the input impedance of an op-amp is low, its input voltage is derived from the input impedance of that op-amp and the output impedance of the preceding device. The low input impedance of an op-amp also affects its feedback loop.
If the output impedance of an op-amp is not zero, its output voltage is derived from the output impedance of that op-amp and the impedance of its load.
In typical applications, however, the input impedance of an op-amp is negligibly large compared with the input impedance of the preceding circuit, and the output impedance is negligibly small compared with the impedance of the subsequent load. Therefore, these impedances usually do not have a significant impact. The same is true of the other parameters shown above.
Take their impacts into consideration when creating a detailed design.