Even with one cubic meter of volume, he could make a construct 1cm x 1cm x 1 kilometer long. There's more than enough material for the chains he used on Arty in 1 cubic meter of volume (especially since it was a charged attack). If it were me, I'd limit the 1 post generation to 2 cubic meters, plus 1 cubic meter more per tick. To be honest though, it's not the amount that is the biggest issue, it's the temperature. Right now it's unspecified but still somewhere in the several thousand degree range, which is too much for a tier 3 when they can use it the way he can.
Regarding the range, are you saying he can no longer launch his spikes or constructs at an opponent? Because launching them would be completely fine, so long as a speed is specified. It was only the instantaneous aspect of his ranged capability that was overpowered.