The black area is where there is no groundplane.
So if there is going to be an arc, it has to go thru the board
to the other side. The thickness of the board is good for
a few kilovolts. I'm sure its not necessary at 30v, but
its trivial to do.
I will increase the size of the cap holes on the amp board.
As far as the voltage references, the linear tech part is a fair
amount more expensive than the ti part. You use one or
the other, not both.