Before I begin, I'd actually offer that this plugin may not be for you. There are numerous plugins for custom post types and meta fields, and this one is for programmers who are very familiar with PHP and are comfortable diving into the plugin's code to see how some of these things work. If you check out the FAQ, I make a few recommendations for other plugins that accomplish the same task. This plugin isn't a great fit for everyone -- in fact, it's only a great fit for a very small percentage of the WordPress population. So if you choose not to use it, I won't be offended :-). That said,
1. The media field type stores the attachment ID. You'd then use that attachment ID as usual.
2. I'm not 100% sure I understand the question, but you can read the wiki for thorough instructions on adding all field types.
3. Language support actually isn't great because of the dynamic nature of this plugin (I thought I had added the i18n support properly, but actually did not). You can override the labels when setting the post type arguments, which is your best bet.