The main page has rules. My post has optional guidelines. They're not official.
As for sound, easy solution is to just make something in Deflemask.
Here's what it uses anyway:
- 2x pulse wave (12.5%, 25%, 50%, 75% duty cycles)
- 1x 32-sample 4-bit wav channel with very limited volume control (best to assume this just does on/off)
- 1x 15-bit/7-bit (selectable) LFSR noise channel, frequencies are kinda weird, if you don't do any freq sweeps you should be fine
Each channel supports hard-panned stereo (left/centre/right).
Volume goes from 0 to 15 inclusive. Not sure what the actual lower/upper bounds are on the period. It appears to be a simple voltage sum, unlike some chips which use logarithmic volumes.
For the curious, at least one pulse channel has a freq sweep unit, and I think both have a volume envelope unit each. You do not actually need to know about these as you can replicate their behaviours manually.