Still here, but preoccupied elsewhere measuring railroad rails.
Do you have a data sheet for your radar module? That is always the first step in applying any unfamiliar device. If you cannot obtain one elsewhere, let me know. I MAY have a data sheet buried under 40 years accumulation of literature, but definitely do not want to launch a search unnecessarily. The spec sheet should give you critical information about voltage and current required and may also provide recommended circuits and horn design principles.
There's really not much involved in applying the modules. Apply power (closely regulated) ;only after you know exactly what is required and get a Doppler signal out. It's then up to you what you want to do with the Doppler signal. It will be a weak squeaking in the audio frequency range with the amplitude and frequency dependent upon what is moving within its beam and how fast. Amplitude is highly variable and dependent upon the strength of the radar return signal, i.e., how large and close the moving target is.
We used our units for measuring vehicle speeds during acoustic noise surveys and, as described in my old post, after frustrating screwing around with the circuitry, after hitting the tuning sweet spot we were able to get useful speed indications off cars several blocks away. On one test, we were able to get speed indications off transit vehicles approaching around bends in tunnels long before they were visible around the bend. Undoubtedly a slam dunk for the radar due to absence of interference from other vehicles, but still impressive (and fun).
As I recall, we tried used an automatic gain control chip but ended up using a fixed gain op-amp circuit on the doppler signal and just allowed it to clip high signals. If I was to do it again I would definitely use a log amplifier IC to handle the large dynamic range of the Doppler signal without danger of bizarre waveform distortions that some overloaded op-amps create. You do get waveform distortion out of a log amp due to the compression of sine wave peaks, but they are clean and do no harm in the subsequent circuitry.
If you are looking for a speed indication, you can apply the compressed signal out of the log amp to an F-to-V converter chip and apply the output of that to a meter with suitable buffering and voltage/current scaling. It may also be feasible to apply the signal to a tachometer mode digital panel meter but I have not tried that. Then you would have to figure out the conversion from frequency to speed in handy units. In professional units they use processing circuits that compare and average several readings frequency readings to verify them before displaying the result.
Remember that the Doppler signal does not contain direction information so, in the absence of special processing to generate an offsetting frequency, you can't distinguish approaching from receding targets.
The size of your horn aperture strongly affects the narrowness of your beam and, therefore, your ability to focus on a specific target among general traffic. The larger the aperture the narrower the beam. The stubby 1" or so horns commonly supplied with the radar modules are intended for intrusion detection applications and provide almost no directionality. As I recall, the horn I fabbed from brass sheet and angle from the hobby shop was about 10" long and about 5" across the mouth and provided good directionality. Research radar horn design, as aspect ratio and flare rate affect your results.