New role only view but create once

I need to create a new role that can only add a post once to a custom post type and then only view it and comment on it. The purpose is for a vendor directory, I want them to be able to create a user account which submits form fields and creates a new post and assigns them as the author but restricts them from being able to modify the post. Can anyone point me in the direction of how to achieve this? Thanks.