Oh - I just saw "Create -> Import from scanner/camera" on the GIMP menu. It uses the TWAIN driver that should be available for most scanners.
When it comes to image size on screen, GIMP really takes a turn. Just use it some. I used Adobe Photoshop a lot and really liked it, but Adobe has priced themselves out of my needs. I am annoyed at how terrible the GIMP help is, though I am likely behind on releases; I usually use Google search and describe what I am seeing/wanting to do and quite often the answer is easily found.
When you say "import" is this just by Opening the file? Or are you saying "New"?
It should default to the size of the image; maybe the software didn't actually crop it? I've seen that before.
People used to do that in MS Word all the time and all Word was doing was marking areas not to display. I'd get a 2 page report that had a little image on it and it was 20MB at a time when floppy disks were still in common use. Find the picture and it's 10 times the size of the page with only a little bit exposed. Tell Word to reduce and it became like a 10 kB file.