1. Yes, I am one of those people who says "a couple" is TWO. Period, end of story, I don't care what you think. (Also, re the mouseover text: One. One space. FOR THE LOVE OF ALL THAT SPARKLES, ONLY ONE. Signed, your friendly neighborhood copy editor.)
2. A few: Three or four. Maybe five if I'm feeling benevolent that day or if you claim to be really bad at subitizing. (As an aside: It drives me nuts in novels when the author writes "There were three or four people in the room" or something like that. Which is it? It's not THAT hard to tell the difference between three and four.)
3. Several: 5 to 8 or so. Anything more than that is "a lot."
4. A handful: I don't usually use this in the metaphorical sense of "a small quantity." When I do, it straddles the boundary between "a few" and "several." But usually this is what I mean by a handful:
For comparison, this is a fistful:
Handful on left, fistful on right. As you can tell thanks to SCIENCE, a fistful is about twice the size of a handful.
I put some of these back in the bag afterward. "Some" is a quantity I'll leave undefined.