Which one should I use?

Dear All,

I am planning to have a sidebar widget on my website that displays an image with a few lines of description. The image is automatically fetched from a satellite-based source, updated regularly, say daily. I want this widget can be updated from the back-end. So, admin logs in to the dashboard, and then click on the menu (like a custom post type) to update the info. Say the menu will be called “Update Current Traffic info”. The info doesn’t has to be archived like a normal post, because once it’s updated, the old one is not needed anymore.

The “update Current Traffic Info” form will look like this:

+—————-+
++++++++++++++++++
++++ newest +++++
+++++ image ++++++
++++++++++++++++++
++++++++++++++++++
+—————-+

|Fetch new image button|

Description:
___________________________
____________text area_____|

| Update! |

————————————————-

my question are:
1. What best to use for this kind of thing? Is custom post type is the best, or a custom plugin?
2. If it’s custom post, how to display it on the widget (any tutorial or ready use plugin for that?
3. if it’s custom post, how to create the “add new” form look like above scheme, especially to provide the image and ‘fetch new image’ button?
4. If it’s a custom plugin, is there any tutorial or ready to use plugin to do that? Or, can you guys show me how to create the plugin?

Thank you very much.
Your answer is so much appreciated.