Thanks for the responses. A couple thoughts...
This is a four piece blues band with live drums, bass, two electric guitars (one of them doubling on guitar synth) and all four of us singing.
We've struggled with the powered monitors we currently have with feedback and volume issues. I'm pushing to try a Mackie DL1608, which I recently purchased, that will have individual Aux Sends for each monitor. I've been getting other suggestions about speaker placement, and wanted to see what people thought...
I have heard/seen "coffee shop" level systems set up to act as FOH and monitors, but anything with any volume to it (drums, electric guitar) I'd think would push that over the edge...