After you crafted nano - coal is mostly useless.
After you crafted quantum - its gg, nothing to do here anymore, there is no PVP in industrial, no epic devices, nothing.
Since you may generate energy from nothing with no maintance, you actually dont need any more resources.
Due quantum godmode you dont risk loosing anything, soo you actually nowhere to spent resources.
Suggestion about pvp is already denied, soo i suggest multystage nano-quantum.
When you craft nano or quantum is have only very limited max durability 1-10 HPs, you may recharge it (with full energy cost for this 10 HPs, 1kk just for few hits for quantum) and it wont break completely.
To increase max durability you must invest resources, you shoud be allowed to invest any type of matter (with different effects), this shoud be handled by nanoforge machine.
Armor system shoud adsorb damage, not hits, soo TNT blast will deal much more damage then arrow.
Using carbon-iridium plates shoud have hurge bonus, to encourage it's mass production.
This will make game a lot longer and PVP intensive, since ever when you crafted nano, it wont grant you godmode right from begining, and users of suits not equal due max durability difference.
Nanosaber shoud have similar upgrade ability, with damage scale.