4. Yes and no. The .223 Rem & 5.56 NATO are externally the same, occasionally give or take a few thousands in non-critical areas. The primary difference is brass thickness... the 5.56 NATO brass being thicker than .223 and for a given powder charge, you will have higher pressures. Refer to you're reloading manual.
This is not necessarily true. Sierra makes no mention of this difference in their 223 bolt and AR articles, while they certainly do for 308. In 223/5.56 there happens to be very little spread between brass makers, including commercial and military.
Further, here are some actual measurements to demonstrate this is not true at all, at least not consistently among different manufacturers of military cases (Radway is UK, Hirt. is Austrian, etc.). You will see that Lake City 06 actually have the highest capacity.
If you study that table you will note that both the weight and capacity of the cases is markedly similar, within ~2% for case weight, and water capacity, with military cases interspersed throughout the spread. IMO there is no need, or reason, to use different loads between military and commercial 223.