Yeah, I guess the important takeaway from the Poison scene is that he's pretty apathetic in the face of this huge, repulsively evil creature. It's really not a far cry from the scene where DMC1 Dante first encounters the Griffon--"Flock off, feather face! Or you can stick around and find out the hard way!"
You might also interpret his responding in kind (remember, Poison says it first) as a way to illustrate his youth. It's a bit of an immature reaction, but not an unrealistic one for a young man (teenager?) trying to prove he's tough when he may or may not even know how tough he actually is. Remember high school? There was kind of a lot of that.
Therein lies that vulnerability I mentioned. It just so happens that he is, in fact, incredibly freaking tough. He just doesn't quite handle himself with the 100% coolness of an experienced adult (see DMC1 Dante).
>Aquila question
Nope, the "Feed" ability, as it's called, is unique to the Osiris.
>DLC question
I'm actually not sure what the answer to that is--which is to say I've never heard it mentioned in DLC plans. Can't really give a 100% sure answer here, but I'll definitely give an update if I get one (and am given the okay to talk about it ^^;
. Also keep in mind that you can start earning yourself some orbs right now with the iOS/Android app, so if you're not planning to get the pre-order bonuses, that's an alternative option.