I need to give the file a unique name that depends on the original image. There's no way to automate the naming.
Ok for this you probably need to use the post-capture dialog. Though note that there are some tweak options you can set to make that easier -- like making the dialog start with focus in the "Override filename" field -- I'm not sure if you are using that feature or using the "Save image as.." function. The former is quicker. You should be able to just type the name into that field and hit enter and be done (having it copy the image to the clipboard automatically after that).
You can also use the Thumbnail button to quickly make a thumbnail of your target size. First use the thumbnail dialog via main menu File -> Create thumbnail and set the option you want. After that you can just hit the Thumbnail button on the main toolbar.
If you need to make a thumbnail automatically after EVERY capture, you could use an external commandline tool for that and configure it to run after every capture, on the "Post-Capture Options" tab.