^ Yes, definitely make sure flash and sound are off haha
When taking photos of the exterior of a building, I always do it as I am leaving. That way even if they do see you, your interaction with them is already completed.
Nobody can tell if you are using your front or rear-facing camera. To make it look more like I'm taking a selfie when I'm not, sometimes I will adjust my hair and smile or pose at the camera. These days, people always have their phones glued to their hands and take pictures of everything, so I doubt it raises much suspicion.