FFT looking messy after filtering process
If your description is correct, you are seeing noise.

After step 1, everything above 2 kHz should be gone. After your band-bass everything below 8750 Hz is gone, so you basically end up with a null set. Since your filters are not infinitely steep there is still something non-zero left over but it's mostly going to be noise and very poorly defined.

Rectification is also a highly non-linear operation, so chances are you also going to get some aliasing in there as well.