I supose it depends what sort of situation would arrise during the WWI era had the roman empire remained.
All that ceremonial armour would be not much use in a WWI trenches type combat, other than to protect vital areas from shrapnel. Also It would be very expensive to produce that much armour for a regular conscripted force.
However, if the unit represented an elite unit, such as a guards or semi police or paramilitary role unit (such as a colonial police force) the armour would be good just as decoration. Probably highly polished steel or gold plated tin. Also as a colonial police unit the armour would be usefull against rocks and stones or knives or whatever else protestors could get hold of.
The fact is, that armour has evolved from different styles, taking a form apropriate to its role and the array of weapons aranged against it. The type of segmented armour worn by romans of that early time would have been replaced by medieaval fitted plate armour in response to the use of pikes and pole arms, and the extra cost would have left the foot soldiers (probably armed with complicated crossbows and pole arms, the romas always favoured the technological solution) with little or no armour, just as actualy occured in a europe without the roman empire.
However, the romans, and later the italians were always devoted to tradition (an intact roman empire would almost certainly have been home to an intact catholic church, the home of conservatism and tradition), and ceremonial armour would undoubtedly have recalled its earlier ages of glory.
I say keep the armour, though even an elite guards unit would favour a darker, ornately etched style when an in actual combat situation. The helmet looks good, though a decorative plume would be a cheap and impressive addition, though they might use black cockerel feathers like the italian infantry of WWI and II.
I think the sword is a good addition, though it would probably be stowed at the small of the back along with the bed roll unless the unit was on parade, where it is now would cause some trouble with handling his rifle.
that's why I said that the unit will look wicked (which ever way it will turn out). The impression of my visit to the IWM is still so fresh I just wanted to share it 
) that since he's making this unit WWI-style, that he'll be armed with a Mauser-style bolt action rifle, although it is entirely possible that it could be autoloading or lever action, since those were both available and, to a limited extent used by several of the armies in WWI (The American Marines used the Browning Automatic Rifle in the battle of Belleau Wood and several other key engagements late in the conflict and the Russians had, immediately prior to the war, ordered 100,000 Winchester Model 1895 Lever action rifles chambered in 7.62x53mm Russian for the Imperial Army). 
