As you said, check your user group settings to make sure Require Moderation is turned off for specific groups.
The admin panel is either in showphoto.php or showphoto.tmpl - cant remember offhand.
Must be registered to view images, so didn't see it.
I use 800 for medium images and 150kb which covers most decent JPGs. I allow bigger sizes for different groups. Sometimes I upload files from my camera which can be 1mb-3mb, so it all depends on your own needs.
Please do not PM me for support or sales questions. Thank you for your understanding.