Campaigns often conduct private polling that they pay for, why should this be illegal? I don't see anything wrong in that email - all it means is that they wanted to get more resolution for certain demographics, I think.
No, they didn't want "more resolution" for "certain demographics". They wanted these demographics overrepresented in the final sample, without disclosing the fact they are overrepresented. These are polls for external consumption, the kinds you'd then find on CNN, HuffPo and MSNBC. I'm sure they also had their own private polls which, while probably also cooked, were more accurate.