In Ear Monitor Advice:
With in ear monitors, you have several approaches for the best possible sound. If you're vocal conscious, you need to have a direct from the PA/monitor mix so you can adjust your own sound without the need of relying (solely) on a soundman (if you have or need one at all) and if you have trouble hearing the amps (speakers) onstage, all you have to do is set up a binaural mike set up (left and right) to hear that stuff and again, set the volume to balance your own specifications. Take notes on the settings when you get them, keep EVERYTHING constant and most of all, DO NOT increase the volume or frequencies on the high end. I ended up doing this in the studio and lost a certain amount of highs in my hearing and this became permanent. In ears are the best if you're a vocal and vocal harmony nut as the chances for feedback are practically NILL.
If you do a separate or different mix from the electric norm- say...acoustic, you might 1) want to run everything through this instead of just vocals in order to hear the lesser volumed acoustic stuff better and also provide a stereo mix, at least for the instruments alone while the vocals would or could be set in mono to help distinguish the two.