Egghead is fine and so is Whirwind but I think a simple but effective story for 1st film needs to be in place.
I have looked at the characters Ant Man has faced and Porcupine maybe could get a look in as first villain & also if not enough of threat throw in Radioactive Man or even as main villain and Porcupine side enemy.
Alexander Gentry was originally a scientist who worked as a weapons designer for the United States Army. He conceived the idea of designing a battle-suit in imitation of a porcupine: it would be covered with quill-like projections for defense. Moreover, it would be able to shoot its quills, or gases, flames, chemicals, paralysis-inducing pellets, or weapons from quill-like tubes, at an opponent. Gentry spends months working overtime to create his porcupine battle-suit. He is proud of his achievement when the suit was finished, and believes his invention is worth a fortune. Yet Gentry also believes that the government would pay him, one of its employees, virtually nothing for his creation. Angrily, Gentry decides to keep the porcupine battle-suit and to use it to become wealthy through crime. Thus Gentry became the Porcupine, one of the first costumed professional criminals of his generation.
Hank Pym, who was then the original Ant-Man, and his partner, Janet van Dyne, the Wasp, soon defeat the Porcupine while he attempted to rob a bank.[1] However, the Porcupine succeeds in escaping. After Pym had also assumed the superhuman powers and identity of Giant-Man, Porcupine returns for revenge. During the resulting battle, the Porcupine consumes what he thinks is a Giant-Man growth medium, but which instead shrinks him to microscopic size