Thanks to all who chipped in to help. I currently owned the Z1 for about 4 days. While I previously owned an Android phone, I am totally new to the Sony smartphones as well as their file systems.
Part of the reason why I chose to buy to this phone is the apparent ease of root. However, it seems that that is not the case. 4.3 apparently is not rootable with 1-click. Compounded by the fact is that there is some sort of unique identifier in this TA partition (whatever that is).
Please treat me as a noob and answer my queries with as much info as possible.
Believe me when I said I have done my fair share of reading and trying to understand what is the entire process all about, I am still not really making any sense of most of it. There is only so much Google can do for you before you start seeking personalised advice.
Now, from what I gathered in this thread, I apparently need to:
1. Downgrade to 4.2.2 (.534) firmware, using a FTF posted by someone called Nuts. I need to do this 'cos I don't want to lose my IMEI, which is some sort of bug.
2. I then need to root it with a software called "Root_with_Restore_by_Bin4ry". Apparently, Bin4ry is a person and not a software.
3. Then in order to upgrade to 4.3 (.136), I need to flash a special FTF/ZIP by made by Nuts again, using the unofficial Flashtool.
Am I right so far?
If I flash that special FTF/ZIP, does it deviate my Z1 from stock ROM? Can I still get FOTA updates?
Can I do all this without unlocking the bootloader?