Either of your solutions would work I think. Either that or have another empty slot open up when you have used the first three because at the moment after that you have to open the tag editor, add the image, save & close the editor, then open the tag editor again and repeat for each image which is extremely long winded when you have a whole scanned booklet or something.
I suppose with actually adding a batch of files (dragging and dropping or selecting multiples) you lose the ability to define how to attach them, unless you want them all to be attached the same way (which would be fine for me). I think just getting an extra slot open up without having save/reopen would be easiest/best but I don't know which would be easier from Steven's side.
I didn't think about the downloading side of things, not really sure what to suggest with that.