about hiding the imterface you can either add black boarders which most ppl do or change the screen resolution from like 1920x1440 to something like 1920x1000 and hide the top/bot screen leaving only the gameplay
you cant follow the hero movements because its too much zoomed in, if you have full screen you can zoom in/out depending on the action if theres a team fight etc.
replayseeker afaik had two keys for zoom in/out, keys for rotations, for camera movements. you can make the camera movement much smoother with one option on replayseeker, i mean the add on simple camera or whatever was the name