I reckon I go up to 8 teeth, make them slightly larger and get away with it.

My main limitation is the fact that I can only extrude a 0.4mm wide bead.
So for practical purposes 0.8m is the thinnest tooth I can get away with that would be strong enough to actually be functional.
That said if I used the MYmat carbon fibre reinforced nylon, you might be able to go down to a 0.4mm wide tooth.

With more teeth you lose the gap between them as you go towards the hub, so while you get more teeth, the part that engages the other gears gets shorter.

These are surprisingly tough. I did squash one, but it took a fair bit of pressure.

I had no idea I could print stuff this small.

makes you think an fdm 3d printed wristwatch could be done. But not by me lol