iPhoto to Photos issue
Neither iPhoto nor Photos stores any photos—they are applications which access the photos stored within iPhoto libraries and Photos libraries respectively. The library is what stores the photos, which is what you should be transferring from your backup.

The library is stored by default in your Photos folder within your home folder, and stores all of your photos (providing you are not using referenced masters). Photos (the application) is part of OS X and you should not be restoring it from a backup.