I was using a transfer pipette that wasn't graduated so I couldn't tell you in mL, but I used 6 drops in the 6oz sample to get to the right color, I imagine this will be very variable and would change depend on the beer you were attempting to make red (or brown or opaque black).
Sinmar doesn't impact flavor very noticably (I've never noticed any flavor impact) - the mouthfeel seemed a bit more slick on the sample last night but that hasn't been my typical experience with Sinmar and it could just be that the IPA has changed a bit since my last sample. Or, more likely, it could be the result of the sickness I'm battling.