Areas armor needs to cover are:
Protection factor
Destructive capability
Mobility
Think liquid metal, as in Terminator 2, but without the homicidal tendencies. Then again, it is meant for war.
Add some built in weapons, like the classic disentigrator, stunner, narrow beam cutting laser, light saber, and explosive throwing stars.
Install a good built in sield capable of handling up to 100 vehicle weapon class hits, power absorbed into capacitors to power the shielding and weapons. The kietic energy of incoming rounds would be sucked out by the field leaving a round so slow it could not penetrate the metal skin.
Fit a safe little antimatter power converter to cover normal power needs.
For movement, the metal skin would support the weight of the whole package. High effect grav drive controlled by the troops foot movements. Manuevers seen in HongKong kungfu flying wire movies would be possible. Add in a teleport system may be a bit over the top for TL18, but not TL19.
Install a environment control system capable of handling vacuum or nasty chemicals.
Now for the final reason for liquid metal skin for the armor, camoflage. What is detected as a target can be taken out. The normal appearance of the armor would be a black suit ala M.I.B..
THe armor would change appearance to match local surroundings as an appropriate visual outfit. It would look like a tree in the woods, a rock in the mountains, a civilian in a city, a demon/dragon in a TL 1 area, or whatever the trooper or his CO selected.