Board Stackup

The design leverages a stacking approach.  There were several factors which led to this including:
a) Desire to stay within a small form factor (board costs, workable two layer boards)
b) Desire to avoid expensive board-board connectors (cost and ease of hand construction)
c) Desire to minimize cables (cost, hand construction, tediousness and lack of tooling)
The following stack is used with readily available parts.