Hey there, thank you for the feedback!

Yes, this is completely stiff, no flexible parts. I've experimented with a few gears and different distances between them. I've found that this herringbone gear works very well. I don't experience any visible backlash, but the gearing ratio also helps to suppress that.

I've printed everything from Hobbyking Premium PLA. Just as you've described, the rotation gets smoother after some wear. But even after 30-40 hours of use they still don't seem to become loose at all.

Securing everything on the bearing, there's no visible wobbling. I really recommend using a bearing if possible, it makes things so much easier. (:

Good luck with your project! (;