Recover Android system with TWRP Recovery

Looking at the installation instructions of the ROM you flashed, I am guessing in the TWRP/ CWM options, under Advanced Wipe , one of the options " Wipe Dalvik Cache, Cache, System and Data " (likely data) was missed out leading to the current situation.

[[ Edit

Thanks to OP for confirming that wiping data was missed out by him while installing CM. A couple of other observations made by OP are listed. These are NOT normally observed behaviour of CWM but may be occurring due to incompatibilities of ROM being " unofficial"

1. CM didn't start normally when data partition alone was backed up


2. He had to resort to wiping data to get back to normal functioning. This is also mentioned in the installation instructions of the ROM

Flash CyanogenMod:....Note that the recovery might fail to restore the backup when you want to go back to the stock ROM (emphasis by ROM developer)

]]

That aside, as you brought out, there are two options

Option 1 Re-flash CM ROM and subsequently revert to stock if needed

Option 2 Attempt to flash stock directly

Option 1 would be preferred option since your unable to flash stock ROM and get an error message

Suggested steps for Option 1

1. Boot to recovery mode of TWRP/CWM


2. Wipe Dalvik Cache, Cache, and Data (inside Wipe -> Advanced Wipe for TWRP)


3. Install CM ROM


4. Install the GApps zip-package


5. Test that ROM is correctly installed by testing minimum functionality of Google play store connecting, camera and call/ SMS working

Now,assuming it is successful,use the ROM for a couple of days before deciding if you want to continue with it or revert to stock

Reverting to Stock from CM 12

1. Since you are using OS X and Debian, install Heimdall (am not conversant with it so will skip the details)


2. Flash recovery. This guide seems to explain the process well but you can suggest a better alternative with your experience http://davideddu.org/blog/posts/how-to-flash-a-recovery-image-using-heimdall/

Additional Information that may come in handy for related issues and also to cover points raised in the comments section of question

Windows users:

• Flashing Stock using Odin

Odin has different versions and some of the versions have options changed. Hence, the description in guides may differ with options available on the tool. This guide has a good pictorial description corresponding to newer version of Odin

http://androidmtk.com/flash-samsung-stock-rom-using-odin

• Extracting Stock recovery from stock image

  
  
  

  http://howto.highonandroid.com/samsung-tutorials/how-to-extract-stock-recovery-from-samsung-firmware/2/




• Linux users

Instructions for flashing stock ROM ate covered here How to convert .img to .tar to flash using Samsung odin tool?

• Command line instructions for backing up stock recovery from image
  Can we backup the stock recovery.img in any way?