Hi Mary,
File size of a model using images (photos you've taken) can go up to the skies if you don't optimize your images. It is a simple process you do in a 3rd party application (image editor) when you crop everything off that you don't need in the image, resize it to something "reasonable" (definitely somewhere below 1024 pixels which is generally the "limit" of OpenGL display SU uses anyway) and even save it compressed.
As for your lockup after importing the GE snapshot - it can even be related to your video card/driver which you haven't said anything yet. If it persists, try to go to Window (menu) in SU > Preferences > OpenGL and unable hardware acceleration. If it "seems" to fix your problem, there's definitely something going on with your graphics system (maybe you don't even have a dedicated card just an integrated chipset).