WordPress.org

Do I have to know the coordinates of the locations I am adding

No. The system will ask Google for the coordinates before it's added to the database.

What features will be included in the next version

1. Multilingual support
2. Creation of pages for each location
3. Capability of creating custom maps with different datasets, size and features
4. Embedding custom maps in pages and posts with : [gmapper class="defined_in_admin_panel" data="defined_value_in_your_script"]

I want to add new features, what should I do

You can download and modify the plugin as you wish, as long as you respect the terms of the GPL licence. Please contact the developpers to ensure nobody else is working on the features you want to work on.