The large angels are a nasty bunch as far as territorial issues go(especially the pomacanthus family IME)..Personally i like getting juvis ,,just to watch them change..
Since your getting an angel you might as well go for triggers too
I wouldn't be too concerned with the order because it sounds like your going to have an aggressive set up anyway..The Achilles is known to be fairly aggressive too..
I've been able to add fish long after i had angels in ,,but again,i have an aggressive set up also and only added fish that were not considered timid or shy..I remember adding my koran angel a few years ago,,my purple tang darn near tore him up ,but he held his own and they became buds..
Good luck and enjoy stocking that nice big tank