Wouldn't be better more skirmisher than archers? -just a thought-
You could get rid of 1 archer unit and the portents and have two extra skirmish infantry depends on you prefured style of play.
I generally would go for the extra range and the portents.
This army is from the orginal book and isn't the best that can be done, Rick Priestly has a couple of alternative Late Roman Armies posted on his web site which are more interesting