Upgrading Drupal

About 8 months ago, I installed Drupal. Was quite enjoying it, but then life got busy and I haven't touched it in 5-6 months. I've been getting about 1 email a day to upgrade/update things for a while, but... it wasn't a priority for me atm.

Starting about the day before yesterday, though, I'm getting 26+ emails a day. That annoys me enough to do something about it.

Since upgrading from 7.23 to 7.24 :
I constantly see error messages :

Hi,

I wanted to ask the Drupal Core team if your minor upgrades (especially those including security fixes) are programmed in a defensive way, so that the new code continues to work with the old database schema before running the db updates?

The reason why I am asking is because I would like to be able to update Drupal sites in a load balanced environment with zero downtime. If there are no db changes this makes it easy, once there are db changes involved I guess it depends on how the new code can cope with a not yet updated db.

I was handed a drupal site to maintain because no one else wanted to do it anymore. The more I learned about drupal the more I love it and have built 2 of my own with it so I know alittle but most of it I'm still learning. Anyway, this site was not built with what I think is the proper file structure none of the stuff is in the sites folder they put it all in the core folders. So I moved it all then proceeded to update the site to 6.29 from 6.28. Ran update php then tried to use backup and migrate to restore it but my newest backup was a .tar and said was not allowed on my server.

I keep getting a warning in my status report about /tmp being unprotected. I don't seem to have a /tmp directory relative to the drupal root, and adding the htaccess file to my filesystem's /tmp (which seems unnecessary as its not web accessible anyway) doesn't remove the error. I've also tried creating then protecting a drupalroot/tmp directory but this still doesn't take away the error. Any thoughts?

I have upgraded from 7.22 to 7.24 and realized, that some images are not showing up any longer.

Since only certain image sizes were not available any more, I narrowed it down to the image styles. And indeed, in the styles list, the manually added styles are no longer listed.

when I have opened /config/media/image-styles I get the error message:
Notice: Undefined index: label in theme_image_style_list() (line 671 of mysite.com/modules/image/image.admin.inc)