I am not sure about the first part of your question, but I would be interested in the answer of others.
I know "reports" are that they have sold somewhere between 30-35-40 million albums worldwide.
Then add merchandise from tours, tour tickets, and online merchandise (probably not much online for them).
So if anyone has knowledge of the music industry they could comment on the items above.
As far as your second question, I think there are two answers:
#1 Die hard metal heads that had their thumbs on the metal scene, probably discovered them around British Steel era 1980.
But that most likely did not put them on the mainstream map per say- just among head bangers at that time - most likely.
#2 Screaming for Vengeance in 82 really shot them into the spotlight for financial and music success.
#2a (or #3) If you wanted to say the next level (although controversial) would be Turbo in 1986. Again sold out tours and higher record sales (compared to other albums than SFV), but notably Women & Jocks!!!!!