A: Draw 2 + Doom starts:
“Draw 2 cards per turn plus one for your personal Doom score (combining your Keepers and Creepers), with a maximum of six cards.”
So each person, on their turn would get to Draw 2. Then they would look at what their total Doom points are, and draw as many extra cards as their Doom total. Since it’s not possible to draw a negative number of cards, they simply do not get to draw extra if their Doom total is zero or negative. Nobody will ever be drawing fewer than 2 on their turn.
In short, you don’t have to do the math all at once, it was just easier for us to write the card title that way.