There is no way to turn off commenting for posts on your Business Page. This feature is only available for Groups. You can turn off the ability for other people posting to your Page
The image Download button does not appear if the image is a Cover Photo (in the 'Cover Photos' album). The Download button appears if the image is not a Cover Photo, even if it's uploaded by a non-Facebook friend.
The Chrome extension, DownAlbum or equivalent User/Greasemonkey script for other browsers like Firefox, will allow you to download the full-resolution version of images in the 'Cover Photos' album.
Best Answer
You can't.
References:
The turn off comments is only available in groups:
The current Facebook profile and cover picture would always be public:
You can't disable comments for everyone on your public profile info: