Thanks for this great project. It's awesome!
There is a hard coded 32 on Line 478 and line 502 of fft.vhd.
I tried to compute an FFT of a size other than 64, and it did not work. I got don't cares in a simulator. I replaced the hard coded 32 with (N/2). Now it works for other power of 2 FFT sizes. I only checked a few (16, 32, 64 and 128).