Re: reverse breathing
Based on my understanding only, subject to correction by Those Who Know:
I think this practice it is all about building connections throughout the body using the visualizations of breath coming in and going out through palms of the hands and soles of the feet. When you breathe in, you visualize the hara compressing in on itself, pulling breath and ki in from all directions but especially through the limbs. It is *not* about 6-directions as Dan talks about it; that's another exercise with different visualizations.
You do *not* want the chest to inflate on inhale. It just sits on the hara. Actively pull the diaphragm *down* on the inhale, compressing the hara from above. Raise the pelvic floor, compressing from below. (People say go easy on this because it raises blood pressure; maybe, but you've got a lot of structural weaknesses down there (think about it) that need to be reinforced or you'll have other problems.) Pull the abs in, compressing from the front. I don't generally feel the need to compress from the rear because you have the backbone providing stiffness and you generally want to get more expansion/breath/ki in that area anyway.
Breathing out is the reverse. Hara expands pushing ki out through the same channels as breathing in. This is expansion, not swelling up. Chest expands with the rest of the body but don't puff it out.
Watch out for tension on inhale and exhale. You should be lose and free to move throughout. Joints should not lock up. I find thinking of the breath going through the joint and out the body and across the room helps with this.