I ran a small PA for folk clubs, village halls and the like which consisted of a Phonic PA head (2 x 200w, assignable to main and monitor), 2 1x15 + horn cabs built by a local PA supplier on stands and some really useful little Peavey monitors for places with actual stages as opposed to just a corner of the room. It was just fine for anything from a solo singer to a small group and handled guitars, vocals and keyboards without raising a sweat for 100-200 people. It was nicely self-contained, used only one power point and went in the back of my Vauxhall Cavalier (mid-sized hatchback) with room for my guitar, Fender BJ and the smaller section of the rear seat free.
These days I'd be inclined to use powered cabinets with a small desktop mixer. The plus point is that you only need to carry mic cables for nearly all audio connections. The downside is having to run more power cables.
To avoid the need for monitors, place one of your main speakers behind and to the side of the performer(s). A little experimentation with placement will get you round any feedback problems.