Ninja Spy/Assassin

[harrface]

So I fell in love with being a dark monk, being a Ninja Spy. Then I started seeing Shinato/Acrobats running around, I thought, "What if I swap all of that?" I decided I wanted to make a Ninja Spy/Assassin.
I've never seen one, heard of one, or caught the faintest wiff of a build on the Forums yet, and I'm never good at multiclassing.
Asking three things here, basically:
1. how should his start game be (TRing my monk into this if I get good results from this.
2. How should his end game turn out, at level 20
3. most importantly, will this be a good DPS machine at all? I feel like with sneak attack and his speed and power he should be.

I'm thinking this: Halfling, 13monk/7rogue ninjaspy/assassin. Dex build, uses short swords (GS at level 12) and wraps (for ToD) will spend his time in Wind Stance. Thinking he won't be trap disabling dedicated, but can do traps somewhat. Mostly DPS. Powerful Sneak attacks.
Tips, changes, etc, I want it all