Important is willing to have (in my case, 2.5) on a USB stick, the latest firmware, not as some falsely claiming an older.
Important only if the request comes the Firmware einzuspielen the USB flash drive dock. I had started with the stick, the PS4 and the firmware is not recognized here. At the second start without Stick it went well with no probs.
After having virginal PS4 gestart with firmware 2.5, I then played back my previously backed PS4.
All local games Data were there, all users (my 3 kids) and all DLC Source Files.
That everything was the same again free only with 1.47 TB of storage * happy *