I've read that the threshold for tasting 88% lactic acid is 2ml per gallon. That was attributed to Palmer, I forget the source now. Other folks have recommended no more than 5ml in a 5gal batch. In any case I've never needed to add that much to get my water pH right, although I do utilize my flavor additions (CaCl2 and CaSO4) in the msh to help get the pH down as well. Sounds like you are OK with your addition, assuming it was for 5gal. You can always add a little distilled water to your water to reduce the amount of pH adjustment needed. I'm not sure if preboiling would reduce the alkalinity, it might.
I'm not so familiar with sauermalz, someone else can comment on that.