Sorry if it's not much help but .... whatever works best for you. We've got a 6-channel mixing pad for the instruments with DI, which leads into one channel of a 4-way powered mixer/amp, then microphones into the other channels, and unpowered speakers. The monitors can either come off the mixer pad (instruments only), or from the amplifier (whole mix with voice). Which works best depends on the venue - soft furnishings/drapes absorb sound, hard walls reflect it, lots of people soak it up and so on. Like with most things, there's no golden rule that's right for every occasion. Sorry.

Andrew