First of all thanks for the plugin!
Here are some suggestions:
- allow html in the post limit reach message (e.g. for a "back to admin area" link)
- add option for displaying the "post limit reached" message on top of the admin area (similar to the "WP update available" message) not only after trying to add a new one
- add an option to not hide the add new post link (I removed the code manually) as it could be confusing that it's only removed from the all post overview page but displayed when the user is on other pages (e.g. dashboard).