Is there any way to reuse the same file or image? Is there any way to reuse the same file or image  while uploading 
I just worry about having multiple/duplicate image files on the server - in time it could get full and slow down the server.

I have used FileField Sources module but I think its not compatible with drupal 8 its not showing configuration setup, any other alternative?
The short answer is: Yes!

And you also don't have to wait till 8.4 comes out (however that will make things easier).

I suggest you the following modules:


Media Entity
Media Entity Browser
Media Entity Image


How is it working? (in nutshell):

Instead of using "image fields" you will have reference fields to media entities (Media Entity), which provides you the opportunity to use such an entity multiple times, also by other contents. 
Media Entity Image gives you just a predefined bundle to media entity, which is a nice to have.
Media entity browser gives you a widget, which opens a modal, where you can select from existing media images, or upload a new one!



Drupal 8.4 will provide this as a core feature, which will make it more stable and easier to use. But until then: these three modules also do the job.