Reward videos number of plays limit

Question

I am developing one android game. I am planning to integrate a reward videos in my app. I am planing to go for AdMob mediation. Below is my question.

User can watch a reward video to save his/her life in game. So s and when he/she out, I will show them msg to watch a video and continue. My question is, how many videos I can show to the user? I know we can set the impression and hourly limit in admob dashboard. But still is there any restriction on showing reward ads per day? What if user keep watching the ads many times ?

Thanks you in advance