Author Customization expands core author management with features such as per-post author information and rich user bio editing.
The post author's display name and biographical info are copied from their user profile.
Yes. The plugin saves author info to each post you edit whether or not you've enabled displaying author data from the post metadata. If you decide later that you want per-post author information to be displayed, any post you've created or edited since installing the plugin will already be set up to do this.
Not yet, but that's in the works. I plan to add support for this in a future update.
In order for author information to appear on your posts and pages, the theme you're using must have support for this. If it does, you should see your author info changes without issue. If you know it shows author information but you're not seeing the changes you made using this plugin, pop over to the Support area. If your theme does not have support for author info, contact the theme developer.