Q: Storage issues

Backing up the phone in iTunes on your computer will save the photos inside the camera roll as part of the backup. You can only get them back if you restore your phone from the backup again.

The only way to save the photos to your computer is by importing them, as explained in this article:

Import photos and videos from your iPhone, iPad, or iPod touch - Apple Support

After the import has been finished, you will asked to decide wether to keep the photos on the phone or let iTunes erase them.

Don't forget to delete the photos in the "recently deleted" album on your phone as well.

To find out more about the used space on your device, connect to iTunes on your computer, plug in the phone and have a look at the status bar at the bottom of the page.

If you hover the mouse pointer over the colored parts, you will see the actual size of your photos and other files.

Storage and iCloud usage will only control the size of your backup made to iCloud.

iCloud: iCloud storage and backup overview