Yeah, that’s not ideal. Your thumbnail will be super small and your large images can get super large in terms of file size.
I prefer something like 600 to 800 as max size for the thumbnail and 1500 to 2000 for the large images. But that depends on what you are doing on your site.
If the thumbnails are too small or the large ones too big, there is a setting to choose which ones to use for the grid view. Of course if both have problems, I can’t help you.
If you change the image settings for the database you would have to upload the image again.
The images are centered and scaled up or down to fill the container in both direction. So you want the aspect ratio of your uploads close to the aspect ratio you set for SuperGrid. So try to set it that way and try to keep all uploads similar. The more you deviate from the default aspect ratio you set, the more will be cut off from the image.