Steve,

Will U5 get hot? I usually use a larger pad as a heat sink.
Is there much power lost in Q2,3,4,5? I usually have a large collector pad on all layers. This works as a heat sink and carries the heat to the other side of the board.

U3,C12 spacing?

Often a LCD display needs a “pot” to set contrast.

Mounting holes?

When I do 4 layer boards I usually use one of the inter layers as ground.
The other inter layer may have large areas of +5, +3.3 and a hand full of hard to rout traces. I usually have signal traces on the outside.

If there are noise issues, I may have the outside layers as ground and power planes. This sandwiches the signal traces between planes of copper. (FCC issues)

Using ball-grid arrays I need two signal layers, power, ground, and two more signal layers.

ron