1) go carbon. not a lot of people use stainless yanagiba. You are going for ultimate sharpness with these things and you will sharpen every shift that you are working fish (or at least touch up on finishing stones). Carbon is way easier to sharpen and will make your life better. Yes you have to clean your knife. At least you're cutting protein and not something acidic.
2) Get the longest you can afford to get through your fish in one slice. 270mm - 300mm is pretty normal.
3) Buy from a reputable vendor. All things perfect these things can still warp, delaminate, etc. Especially on the budget end of yanagiba you see more problems. You want a vendor that has strict quality first and replaces if it would even come to that.
4) Single bevel knives need to be 'opened' if you haven't sharpened these things before leave it to a pro it will be easier to follow their sharpening after. JKI and Korin both can do initial sharpening for you.
I recommend either the house brand shiro ko kasumi ones from Korin or the Gesshin Uraku from JKI. Yeah theres some upcharge for being a lefty.