I just started doing something myself. [0] RC2014 is a solid base, but doing the hardware yourself adds even more fun. I am currently waiting for my PCBs and then will start to assemble and program the thing.
I really like how the RC2014 is laid out. Maybe from a "walk before I run" standpoint I should build one for the experience then make my own expansions cards from there.
[0] https://github.com/jhbruhn/CPD-80