What Simon said (and I assume that you meant 4 12x16s, not 12 12x16s), but w/ a caveat. Doing it the way that you describe will break up the continuity of the image, BUT that is OK if you want to do that. Maybe hang them out of order, or have one somewhat above the other, one below, etc. If you're going to break up the continuity, may as well really do it. But I like your idea, and really, whatever we all say here is just talk. You have to visually see it before actually knowing whether it will work or not. Why not try it on a smaller scale first and see what you get? Those frame bars are going to be more of an integral part of the work, so how you frame and colour them will be of importance.
Me, I would simply cut up a smaller print and try different frames (scaled down for the smaller print) to see if a bigger work is viable. This sort of thing is totally dependent on what the image is. Many images will not work out, for one reason or another. Depending on how small your mock up is, you could use painted wooden coffee stirrers for frames, or keep them au natural for that rustic look. If you prefer more frame than that, a thrift store run will net you lots of $1 frames that you can take apart, or use as is.