FWIW, the foam wall tecnique has its own set of issues (nothing is free). first of all, the foam is kinda pricy, secondly, it's not easy to work with, and finally, you need to attach it to the tank as the stuff has a tendency to float (it frequently pops off or just doesn't stick), even with LR embedded in it.
i've seen a few that look nice, but many simply look like a big mass of grey stuff with some LR stuck into it.
i'd definitely do some research and look at lots of pix of how folks have done it, and whether or not you like the look.
as for stacking LR, there is indeed a "knack" for it that comes with experience. the best way to do it is to lay out all your LR and see what shapes you have to work with. this is one reason why i never simply buy a box of LR...i like to pick my shapes and sizes based on what i'm trying to accomplish.
in fact, sometimes i buy interesting pieces of LR for future use and toss them in a 55 gal tank of SW with a couple of pumps for use later. i realize that most peeps don't have that resource, nor do they set up as many systems as us, but you can also dry the rock out and let it die for later use.
