Dear Madam or Sir,
I have great experience in Python, C++, Matlab and Java. Moreover, as a mathematician and software developer, I have am familiar with the theoretical as well as the practical part of the Fourier Transformation.
Python is exactly the right language for this task if you do not want to do it realtime. Is it true that you it should not performed realtime, i.e. the data is transformed without a delay and without buffering?
Moreover, I am a little bit concerned about that the audio file should be chunked, the transformed via FFT into the frequency domain, and the resynthesized. This will produce a lot of artefacts. I would suggest using at least a window function.
Furthermore, there are many other open questions that need to be answered to assess you problem:
What do you mean exactly by re-synthesizing? Do you want to perform a transformation form the frequency domain back into the time domain (Reverse FFT)? Moreover, what exactly should be done with the frequency, amplitude and phase? Should a transformation be applied before resynthesizing?
I am sure that when I understand your requirements I can provide a fast and professional solution. MacOS should not be a problem. If you need a small GUI that you can use with your mouse, that is possible too using Qt for Python.
I am looking forward to discuss everything in the chat.
Best regards