Sorry for the late reply.

I wash my face first.

I currently use it only in the morning. At one point I was using it day and night, it kinda depends on the season for me. I grab 3 dime sized amounts of benzoyl peroxide 10. One on my forehead. One on each cheek. A tiny amount for my nose and between my eyebrows.

I don't think there would be an interaction. I don't use salicylic acid myself, but I use BP while being on Prozac. Your pharmacist or doctor would be the best person to ask though.