What would be the best way to set a compressor/limiter for use with PSM's?
The exact set-up varies dramatically depending upon the model of the compressor/limiter.
We suggest an experimental approach. As a source, use a CD player and a CD of your music or a similar type. Monitor the CD via your entire in-ear signal chain and adjust the compressor/limiter (based on the manufacturer's instructions) to your liking.
Next, try these settings during a rehearsal and see if they work. If not, re-adjust.
Finally, use the rehearsal settings for a gig, and tweak as necessary.