Cold Brewed Coffee - Technique and Sanitation?

Hey All -

I am looking to add some cold brewed coffee or expresso to the stout I brewed.

I am going to add it to the secondary.

I was going to cold brew (with bottled water) in the fridge for 12 hours and then add to the secondary at racking.

QUESTIONS
1) Do I need to worry about sanitation issues with any of these steps?
2) Is 12 hours long enough for the cold brewing?
3) Fridge or just room temp?

Thanks!

All I did was make a cold brewed coffee as usual and dumped into secondary along with about 3 oz of whole beans.