A519a No.

A519b

I'm not completely certain. CMD is a lot like AC, it even goes so far as to say that "Any penalties to a creature's AC also apply to its CMD." I would like to say "yes", but it doesn't explicitly say so anywhere in the RAW and Paizo is very careful not to give its creatures and NPCs too much Dex, so there's no official stat blocks (that I could find at a glance) to support that.

A520a I would go with Bard, it's based on spell progression.

A520b Not as far as I know, but some classes (such as summoner) may craft potions of spells that would otherwise be higher than 3rd level for other casters.