We use the Mackie system too. The passive board16 channel, and and active tops with subs separate for when we need 'em. I have JBL's myself, the Mackie's are superior. My bass player has Peavey, The JBL's and Mackie's are both superior. We do have a couple of Behringer Monitors that are fine, but monitors don't get pushed the way mains do. An old saying comes to mind, and not to say things won't work out fine if you go the way you posed originally, but for what it's worth...
"The sweetness of low cost will soon be overshadowed by the bitterness of poor quality"
with some things it just doesn't matter, i think the Behringers are fine for monitors, it's not what the audience is hearing, and we can hear them well enough to stay in key on harmonies, it's those mains and that board that everything runs out through to the audience that is "your sound". Good luck with it John, I know it's not an inexpensive proposition either way...check e-bay, maybe there's a way to pick up some good Mackie gear at Behringer prices?
All that said, in our small beaches community we do throw downs at parties here and there,guys from this band or that band etc, with whatever PA somebody has set up, the crowd doesn't seem to actually notice or care...ha...other than the occasional techie guy, who'll ask what year is that amp or something to that effect? ya know, so it is just gear...see ya...Moker