Details are being blocked in, and quick prototypes are being built.
Here's how the PCB is shaping up:
Outer diameter is 70mm. The LEDs are 0805 side-mount LEDs, blue on the right, green on the left. The centre shaft is 3mm, and will not go all the way through the PCB.
Tentatively using 3 LR44 batteries stacked vertically in the centre, but I'm open to suggestions, both in battery and in mounting options.
Ideally there's a completely off-the-shelf solution that holds them vertically in the centre, so that the PCB remains balanced while spinning.