I am getting thin scratches that show up with the light reflection
That might be the case. im not sure what your using?
Yes, tell us what you've used so far.
What about if I use cotton ball with synthetic stone slurry? I am thinking Rika 5k then Hakka slurry, then finger stone.
That sounds fine, or at least it wouldn't do any harm. If I remember, your hakka is more on the coarser side (I could be wrong). However, slurry can break down and be fine and finer too. I have uchigumori fingers and also a large size that I can polish on, and - without checking - I'm not sure if you used uchigumori that it would be much finer than hakka, although it wouldn't be coarser. Are you talking about using uchigumore fingerstones?