Obtain Envelope and Pitch curves of my Singing Voice
A zero-padded FFT is not the best method for accurately estimating musical pitch in (near)real-time.  I suggest researching other pitch detection/estimation algorithms (lots of literature and research papers), such as interpolated autocorrelation, AMDF, YAAPT, cepstrum, harmonic product, phase vocoder, and etc., and see if one of those algorithms better meets your exact requirements.
Once you have a pitch estimate, you can sum the waveform energy over a single or small integer number of pitch periods, as that will include all the harmonics, even if fundamental frequency energy is low or missing.  Using an integer number of periods will reduce the amounts windowing artifacts (scalloping or so-called &quot;leakage&quot;) that can appear in a non-integer-period-multiple sized FFT magnitude.
Hilbert methods of measuring envelopes work best for narrow-band signals, but where one does not know or can not extract the exact periodicity.  And a human singing voice is rarely, if ever, narrow-band.
The &quot;attack&quot; portion of a pitched vocalization may not only be rich in harmonics, but temporarily ambiguous in pitch (e.g. not purely periodic, even disregarding envelope).