1) No, because it's far beyond the LPC213x speed capabilities.
The original code is performing it's sampled operation at an interrupt frequency of 8 kHz. It sounds illusional, to increase it by a factor higher than 5 or 10.
Also the maximum ADC sampling rate of about 400 kHz is basically too low. Nyquist rate isn't sufficient in this case.
I wouldn't think about the implementation details unless it's clear, that the controller can perform the required amount of arithmetics at the sampling frequency.