I would advice asking more specific questions - right now you are basically asking someone to create the entire system for you, which can take a lot of time and can be done in many different ways.
Here’s the way I would approach it:
Create a blueprint that contains the flashlight mesh. Add a point light to this blueprint that points in the right direction
Add this blueprint as a child component and attach it to your character’s hand socket
Then once you are able to attach the flashlight to your character, create a function or event that keeps track of a timer. You want the total battery life to be 5*100 = 500 seconds total. Once 500 have passed you want to turn off the point light in your Flashlight BP.
This is all very general, but again it should get you on the right track.
If you have any questions while you are doing this post on the forums and we will try to help you!