For the first control that interacts with Image Library you can use Image Selector. As for the Generic Content control - it cannot be wrapped as a User Control. You can use RadEditor. You may find the following KB useful- How to wrap a Generic Content control in 3.6 SP1 (it applies for 2.7 version as well).
Width, Height, AlternateText are metadata of a IContent object. You can use content.GetMetaData method to access the width, height, alt text.
Make Sitefinity work best for you.
Progress, Telerik, Sitefinity and certain product names used herein are trademarks or registered trademarks of Progress Software Corporation and/or one of its subsidiaries or affiliates in the U.S. and/or other countries.