Adding someone who's not well known will be bad.
As for Antman, that's cheesy. Sorry. He doesn't fit in the movie.
I'm pretty much with you that the MCU and TASM can co-mingle, but you are way off here. Ant-Man is most certainly an Avenger, in fact he is more of an Avenger than a solo hero. I'd venture to say that we only get one Ant-Man film and then the rest of his appearance will be in Avenger movies.