1: Yes
2: Your current config of the phone
3: Top one is for VIII.II
4: Re-flash the backup containing the original theme.
When you make a backup, it is of your current config of the phone when you made the backup.
If you made one after rooting, before flashing a rom, then it is of your phone without the custom
rom. Make one right now, and it is an exact duplicate of the phone, apps and all.
I have three nandroids, noobVIII.II, Warp OEM2.0, and one of the sugarkang jellybean config.
I can flash back to any one of the three in CWM at any time. Whenever I make major changes, I also make a new nandroid (backup).
They are stored on the sd-card in a folder called clockworkmod. For viewing, and or deleting. If you have CWM.
To install a nandroid (backup) just flash it in your recovery program. CWM or TWRP.