Board design is pretty straightforward. Create footprints for the ATTINY84 and accelerometer (see Parts List for the deets), add test points for the I2C bus (so the Rigol can be connected), and put footprints for the contactors. Nothing special.
The contactors are worth a bit of discussion. See the Parts List for the Digikey part numbers. My concept is to make a small programmer board that mounts the contactor, and press the contacts to the footprint on the ATTINY84 board. The contactors were designed to be used with flex cable, if I read the data sheets correctly. Two versions are being tried. They are very similar, but differ in pin spacing and arrangement, and more importantly, in working height. The contactors are intended to compress to a working height, but no further. If they are compressed until their plastic bodies are flat against the board, the contacts will be permanently deformed and will only work once. The key is to keep the contactor bodies spaced away from the circuit board and for this I will 3D print a small spacer. This spacer will have a notch in it that will align with a notch in the board to be programmed to position the contacts. I'm planning to start off with a spacer that only allows a small amount of contact, then increase this as necessary until reliable programming results (hopefully!).
The board designs are complete (ATTINY84 plus 2 programmers) and have been shipped to OSHPark. While I'm waiting for them, I'll design the battery holder and work on accelerometer code.