Four layer PCB layout suggestions
Being as you have put your design up for review let me high light two areas where there is no reason to have such sloppy connections to your microcontroller pads. You should make traces come off the pads at same width of the pads and then possibly widen if you should so desire. 

Example 1:



Example 2:



You are asking other esoteric questions and not even paying attention to trivial details.