No problem, if your extrusion temp is low enough, printing the opposite orientation with no supports is probably still likely going to work - short overhangs usually come out alright in PLA even though the fillet there is a little harder to print (steeper overhang angle) than a chamfer.
For the knurling, yeah I think slowing down (specifically the perimeter speed setting) is probably the way to go to get some more clarity (maybe you could try perimeter acceleration, too). They'd be perfectly usable as is, the randomness of it would probably grip quite well, but you're probably seeing a little ringing on the axis or backlash from the belt tensioning that's just making it a bit inaccurate and slowing down should help with both.
I wonder if it's just the way the stl file was exported? The knob's original designer used a different program to export, I used Fusion360, and maybe there's just something in the formatting of the file that's different and that Simplify3D doesn't like. There's actually a chance that getting blender or meshmixer or something could be valuable in that case, so for any stls with issues, you just import them to the other program, then reexport. Since they probably don't save in exactly the same format, it could fix the thing the slicer doesn't like.