hello, i am an open cart specialist and can create such module, let me explain what you want from module-
users can upload the images and also can adjust the size of image as just like on online shooping site we can adjust the different aspects of items, it will be frontend, now let me explain the backend feature, u can edit the max upload size, image type like jpg, png etc. and on frontend user will be able to upload only that type of images, for point 2 i need you to explain it more... all saved files will be displayed under order details, you can check the module on w3c, there will be no errors in the coding of module, and thumbnails of images must be display when user will go for checkout....