Exactly how are you doing step 1? Never heard of a FileObject viewer. Do you mean a web viewer or are you using a container field?
What kind of files are you working with? The only files that I know of where you can get a file size are image files. Other file types may require a plug in before you can get the file size.
3) If you have the file path to the file, you can use it to insert a file into a container field. You can then use export field contents to export a copy to a new location, effectively moving the file from one location to another. (And export field contents can be used to delete files as well as to export copies.)
For example: when I click the 'Export File' button, it will save the file to the decided direction.
The direction should be: [current drive] / [Category] / [SubCategory] / [the file name of the inserted file]
it will save the file to the decided direction
Who "decides"? the script or the user who clicked the button?
The box above these buttons is a container field named "File", BTW.
If the image in Picture was originally inserted with the Insert Picture menu option (Or scripted equivalent) AND the "store a reference" option was specified, then there is a calculation you can use to extract the pixel dimensions of the image (such as 2000 x 5000 ). If the Store a Reference option was not used, Length( File ) will return the size of the image.
With the layout that you show, do you have File Path correctly showing the current location of the file or will this be used to specify the destination to which you intend to export the file in the container field?