Remove the Glare nodes in the compositor.  The Glare nodes can sometimes cause overbright spots or artifacts on certain frames due to the bloom and volumetrics effects in Eevee.  You can simply remove the glare nodes for more predictable results.

The scene was specifically set up to render with Eevee.  However, it can render in Cycles too.  I recommend removing the volumetric cube and animated smoke effect for Cycles rendering to keep render time reasonable.

Of course!  Changing the resolution dimensions in the Output Properties will not affect the animation properties.  However, the keyframes of the animated rotation depend on the FPS (60 frames per second).  Changing the frame rate will impact the keyframes of the animation.  The scene is created to work with a 60 fps Frame Rate.

No.  The FBX version is only a static model of the disco ball.  None of the animation effects or keyframes were baked into the FBX version.  However, the texture maps are packed with the FBX version and will unpack when you load it into a software application.