To your first question yes Shuriken are viable with quickdraw, shuriken expertise, rapid shot and the poison ability from ninja spy. Outside of that stacking sneak attack is good and as such halflings easily come out ahead of dark elves for pure monk shuriken builds and if you don't get the Spy capstone halflings are loads better. Picking up Deepwood sniper from ranger will get you an increase to your SA range and more SA, assassin and rogue will get you more SA and a second poison ability to use with short swords.
I have a 12 monk 6 ranger 2 rogue build that will transfer over perfectly to both cut it up in melee and be a perfect shuriken thrower.
For your second bit I have suggested in another thread that the henshin capstone should at least have the 15% competence bonus to melee haste and it would be nice if it had a double strike component too. In addition I would really like to see level 1 core allow Henshin to use Wisdom to hit with qstaff and level 6 Core to damage to give you other options. That being said with Over Crit requiring 23 strength it may be a bad way to go.