i also just built a Tiny Nin deck. i took similar approach, with me taking creatures and drawing off them. i think you want to maybe consider cards like, Blue Sun's Zenith Red Sun's Zenith Threads of Disloyalty Overtaker and Charisma + Nin, the Pain Artist is pretty good. im not sure if you wanna play counter spells that cause your opponent to draw like. you wanna play more well Counterspell.

Red Sun and Blue Sun were on the chopping block because their additional effect, while normally awesome, is to be shuffled back into my library instead of hit the graveyard to pump Spellheart. Crater's Claws and Banefire do the same thing but have better effects and there are cheaper draw engines. I could always side them in vs. mill, tho.

I'm not too sure about permanently stealing creatures. While also great, it forces a decision to possibly not use Nin's strength, which is steal, attack, kill, draw. That said, I am really considering Charisma. Great suggestion! Now how about some cards to take out! ;-)