regarding the question of national vs state-level polling, you certainly want to look at state-level polling as superior to national polling, and it is a basic mistake to suggest otherwise. i don't know how else to put it: that is simply wrong. any prof would mark a giant red X over it. 

it is also the same mistake that the media made in 2016.

what you do when you try to distribute national polling to state-level polling is make a bunch of crazy assumptions, like that black people in georgia are similar to black people in illinois because they're black, then try to force racist generalizations on to micro-demographics. again, these are misapplied techniques used in branding and marketing, they are not designed for politics. the statisticians actually doing this should know better and they will admit it if you prod them and ask them the right questions, but they're getting paid to do a certain thing, and most of them don't give a fuck.