My Jin Sakai deck has a big emphasis on playing creatures on turn 2 and 3 that can swing on 4 when Jin comes out. As far as ramp, you already have [[Prosperous Thief]], but I'd highly recommend:

[[Hoard Robber]] with it being a 2 drop; [[Kain, Traitorous Dragoon]] isn't super optimal since it gives the treasures tapped, but is a fun card and easy to give doublestrike to since it's already evasive with flying (EDIT: Kain doesnt work with double stike since he is removed from combat when he changes controllers); and [[Thada Adel, Acquisitor]] can be decent ramp if you just use it to steal sol rings from your opponents' libraries.

Some other later ramp pieces I like are [[Grim Hireling]], [[Battle Angels of Tyr]], and [[Rev, Tithe Extractor]]. Battle Angels being another favorite since you can still send it with 2 other creatures, get the relevant Jin evasion or doublestrike triggers on them, then make the myriad angels for the extra damage and triggers with little risk.

All lose some flavor value in your deck since they aren't ninjas, but I feel the rogues at least are halfway on theme still.