Recently I made my first Japanese sim, Katashi Kito, using my default replacement Ephemera skin (V2) https://i.imgur.com/8ahKw0B.jpg https://i.imgur.com/FkgWVzW.jpg he looks Japanese sometimes ...
For skin, I use KB_HDIcedStarfruit-Epicanthic_ND-Skin. I usually go for a common look as in dark eyes and hair. Though, children can look different depending on their parents. Here are some examples. https://s25.postimg.cc/bgzfbxhnj/Screenshot-300.jpg https://s25.postimg.cc/622jb3uj3/Screenshot-184.jpg https://s25.postimg.cc/oiwy1iacv/Screenshot-327.jpg
Ren and Jodi were born in-game from the parents I created. https://s25.postimg.cc/woezzm15r/Screenshot-966.jpg https://s25.postimg.cc/jx0tt3z3j/Screenshot-211.jpg https://s25.postimg.cc/j7i1gy8wf/Screenshot-1636.jpg
And this is a Sim without using any 3rd party CC. Though, it still would have been useful to have an epicanthus slider. https://s25.postimg.cc/h1nqmqftb/Screenshot-63.jpg
As far as sliders, I usually go by what looks good to me. Otherwise, I might look online for general visual references like I did with my Greek inspired Sims.