ADC and DSP Requirements for FMCW Radar
FMCW radar is a bit tricky, and your "IF frequency is up to 1 MHz" is a bit vague.

In an FMCW system, a target returns a signal that is delayed based on its range. The frequency difference between the transmitted signal and the received signal is a function of that delay and how fast the transmit signal frequency is changing. This frequency difference swings positive and negative, but has a zero mean if the target is stationary. If the target is moving toward or away from the radar, then the mean IF frequency shifts negative or positive, respectively.

The key point is that in order to extract the maximum information from the signal (range rate as well as range), you need to be able to distinguish positive and negative frequencies in the IF, which means that you really need to cover a range of -1 MHz to +1 MHz, or a total bandwidth of 2 MHz.

Nyquist requires that your sampling rate be at least 2&times; your bandwidth, so a 5 Msps ADC would probably be considered "barely adequate". 8-10 Msps would probably make your life a lot easier.