The bolow requires editing of templates. Make you make a back up of the original file before doing any editing!
1. How can I DISABLE LIGHTBOX for NON ADMIN's?
Remove {lightbox} from details.html and thumbnail_bit.html templates. Double check your other templates to see if it is listed anywhere else.
How can I DISABLE the feature to upload THUMBNAILS for NON ADMIN's? I just want them to be able to upload the full size pic and let the script do the thumbnailing..
Delete the thumbnail upload section in member_uploadform.html. After doing this one the admins should use the upload in the ACP if they have a thumbnail they want to load as well as the image.
3. How can I remove that "Receive emails from administrators:" from in the users control panel ?
4. How can I remove that "Hide your online status:" from in the users control panel ?
You can edit this out by editing the member_editprofile.html
I can not answer as I have no issues with the auto thumbnail. All I can say is double check your settings.
As for the last one that is something I never dealt with before, so maybe a more experienced user would know.
Hopefully the ones I did answer help you out a little.