<p>tried searching but couldn't find anything.
I do not have a 3d printer so can't really experiment on my own, which means that when I am going to order a 3d print I want to get it as good as possible. So, my question:</p>

<p>Do quality of geometry matters when 3d printing? Will 3d printer only print quads, or ngons are fine? Are there shapes to avoid?</p>

<p>Cheers :)
M.</p>

I think that you've got the right idea in concept, but benchmarking is typically the best way to prove this out.
You should get in the habit of designing with assembly in mind.
This means:
Hole sizes should be larger than intended and/or shafts should be smaller than intended
Scaling does not always solve the issue! Avoid relying on scale tools as it can result in reducing/enlarging features you did not intend to scale
My own experience has shown that a
clearance
of about
0.005" to 0.010"
(~125μm to ~250μm)
should be enough. However it may be different for your situation with a different printer, filament, climate, etc.
Also consider material shrinkage from the printing process!