I went with the large side with the two oval shaped screw holes against the plate. To play it safe, I instructed the slicer to add tree supports for the holes on the part with round screw holes.

I think somewhere between 80-100% is probably the best call, in addition using PET-G as the material of choice, as this part is near hot parts most of the time. PLA tends to deform easily which in this case is probably not the ideal thing as we're dealing with a component that is used for bed leveling.