First thing that happens is that there's no suspension travel on bumps; they'll tend to steer the car. Not good when cornering and you encounter bumps. Too low and the camber goes real negative. On nice roads, an inch of travel at the bump-stop area would be about minimum; that makes for more travel out where the tires are, but still not much.
A better way to accomplish the lowering would be with drop spindles.
As far as negative camber, I've run as much as -2 degrees with no problems, but that's a cornering setup; in a straight line it'll wear out the inner portion of the tread quicker.