Well, what I normally do which I've found to be a really tidy way of working with galleries in WP, it to use the standard add image feature (but without inserting into post) and then using the function get_attachments in the theme to cycle through... Thus keeping it away from the content.
The problem with this method is there doesn't seem to be a gallery for locations and images (although insertable) don't attach to the posts.
And with the main image, are you saying it needs to be perfect size on upload? Most clients I work with wouldn't know how to do a resize and crop I'm afraid :( any way to run it through the thumbnail cropping scripts? Or maybe just set it as a featured image so I can work with it normally?