Don't think about it too much. If you want to play Scott Lang as Ant-Man, you play Scott Lang as Ant-Man. Don't write a thousand word history explaining the transition. Hank Pym exists, he made the technology and was Ant-Man for a period, now Scott Lang is.

I feel like we're getting bogged down a little, which is my fault given I'm technically in charge, but I want to get this thing started as soon as possible. Let's play, not spend forever talking about playing.