Reader to write one post only. The same as here

Hi,
I want readers to be able to write one post and one post only. I want them to be able to go in and edit that post, if they want to.
The very same as we are doing here.

I do not want them to be able to change or edit any other post, or change any thing through the dashboard. I would also like to be able to let them put Google map onto their posts.

Can you please tell me how this is done.,

Thanks