For future photos, if you use iPhoto, you can turn on Photo Stream so your photos are automatically shared to iPhoto. Then you can delete them from your phone, but they’ll be saved in your iPhoto library.
In iPhoto preferences, you can set it to open iPhoto anytime a camera is connected to the mac, or not to open. Mine is set this way and will automatically ask to import new photos on the iPhone. Of course Photostream has likely already synced those into iPhoto as well, but you will be prompted to import or ignore duplicates. I find that for whatever reason Photostream does not sync every photo, so an occasional plugin to the computer and sync takes care of everything. This is also a good opportunity to edit new photos and sync with my Flickr account.
My first iPhone was a 4 with only 16GB. I bought it primarily to use as my car’s stereo so I checked the data size on my mp3 player, saw I had about 13 or 14 GB of music so I figured that 16GB would be enough. Long story short once I got into using my iPhone for other things I would have to swap out my less popular music and/or apps in order to add new ones. A pain, but easy enough to do with iTunes (and iTunes saves everything). When it came time to upgrade to an iPhone 5 I made sure I got a 64GB this time!
Okay, slightly relevent, why is it that Apple doesn’t give their iPhones the ability to use a memory card that is so common in the Android world? Maybe the new iPhones have changed, but I had one of the early ones (3 I think) and that plus the lack of a removable battery made me give up forever on them and sick with Android. The iPhone was a good phone and all, it just seemed to me that Apple has made a great plan for a revenue steam, need more space you have to upgrade, need a new battery, send it to Apple and for a fee they’ll install a new one. Very customer unfriendly I think.