I did see back around the time he released it, and from that vid I did some reverse engineering, and honestly its just far to fragile IMO. I don't know what kind of voodoo he used, but when I built parts like he did the joints either didn't work or would fall apart if you looked at them funny, and explode if you had to gall to try and pose them. Might have been something to do with my bricks, or maybe I missed something he did, but they just wouldn't work for me. That said his is still an amazing build for sure, but not quite to my tastes function-wise. Also it shoudl be noted that his build is purely for looking like the RX-78, it wouldn't be very easy to convert his design to match other Gundam designs IMO. tkh's design was done with the assumption he'd be building many different Gundams, which is exactly what he did so it seemed more natural to use his as basis.
But anyways, sorry to rattle on, back to Heavyarm's Legs;
I agree larger feet might be more stable, but I think 2x3 plate migth make then too large comapred to the rest of the legs, bu tI'll prolly order the extra parts to do so anyways, just in case.
As far as leg armor goes, its kinda the same situation, due to it's size/scale(I think they're only about 4-5" high or something) I did only just come up with a couple ideas I will try but even if I add flat tiles to side right below the knee joint, it ends up looking pretty fat, but I'll mess with it today and tomorrow and see.
Mike