Cassius I've made an attempt to corelate the current science as presented in the Barrett book with my understanding with the Canon. You're quite right to point out some of the differences! Regarding affect, to me it's useful to think about if and/or how arousal relates to intensity (as I understand it, it's different); I'm also curious to what degree the Greek pathe might correspond to affect.
Regarding behaviors, Joshua had a good point last night about animals that are raised in captivity being unable to survive in the wild. Intuitively (meaning I'm totally guessing!) it seems to me that animal behaviors are driven by pleasure and pain (or affect) and by the faculty of pattern recognition, both interacting with the senses. I think that this is taking materialism to its logical conclusion, although observation would trump any purely logical conclusion and looking at animals seems like a good direction to pursue.
As to Vellius, that brings up the controversy of Cicero being such a tainted source and how much we can trust him. This is why I was interested in reading modern theories in the first place: to try to make up for the uncertainties in the ancient texts and see if that can shed any light on Epicurus' thinking. But as you say, they are two different things.