Those abilities are very different.I doubt it works that way. If Ace sets fire to a building, does he have to use up reserves to maintain the fire? If Magellan covers someone with poison, does he have to use up reserves to maintain the poison on their body? If Mr. 3 creates a lance made of wax, does he have to use up reserves to maintain the wax?
Poison and wax are more or less liquid, and fire is a spreading element. Not to mention they don't have the same added solid element added to them, that Mingo uses for his strings. If they were ordinary strings that he just spawned and left I would get it... but those things are solid and sharp, slicing anything that they touch. I have no doubt that they require strength to enforce, and his focus to maintain it's shape.
Same goes with his clones. If it works like you say they do and he just made them and they never interfered with his reserves, he could just make a army of Mingo clones to patrol the castle so nobody gets in. But instead, he only uses 1 at a time, until that one is defeated.