The window is resizeable. If you are having issues resizing the window, try right clicking on the title bar and then selecting resize.
All erased saves are backed up and can be restored by selecting restore save in the saves menu.
If some files are missing or corrupt you can try verifying the install through Epic Games Store. Right click on the game icon within Steam and select Mange. In the newly opened window, select the Verify Files button. Epic Games Store will then fix the game.
Click the support bubble on this page to submit a support ticket!