if you use the news Modul you have for the short news and for the long news a WYSIWYG Editor field. With the WYSIWYG Editor you can choose the "Insert Image" button and than choos the media dir for the images. With this it should be easy to add and format images to the short news (teasers). This is independent from the group images.
The long text (wich appears when you hit the read more button) opens the same page with the long text. So as i understand you, you wanna have the read more button open not the longtext, it should open an new page. So this is possible with the news modul too. Simply remove in the settings of of the modules the part for the automatic generated read more button and then add the read more button in the short news by using the WB link modul. This makes the long text part of the news modul unnecessary. To make this unvisable you need to tweak the modify.php of the news modul.
So the result for the users is:
1. add the new page
2. add a new news, choose pictures in media dir by using the Editor and a link to the new created page by using WB link from Editor.
Thats all, simple and easy.
What have you to do:
Only make the long text in modify file unvisible, remove the read more part in settings of the modul and explain the above steps your users
This is i think much more easier and faster, then to try to write a own modul, as the news modul brings all what you need.