Defaults the Image Link option to 'none' when adding a picture to a page or post.
Nope. It's ready to go right out of the box.
When adding a photo, under the 'Image Link' option, choose 'File URL'
WordPress' default setting is to link images to themselves.
No it does not. You will have to manually remove links off of existing images. You could also just install this plugin when first setting up the site.