[Q] C6602 MENA Android 4.3 topic

First of all, sorry for my english, it`s not my native language... If i make a mistake just correct me, Thanks !
I`m very noob in Xperia Smartphones...

The point is that i have a few questions about using flashtools with my Xperia Z C6602:

Device: Xperia Z C6602 UNBRANDED
SO: Android 4.2.2
Customization Version: 1270-7937

1-Where i can download Stock JB 4.3 for USA or Europe (For C6602, not C6603)?
2-Is there a problem if i flash a Rom with diferent customization number which i already have?
3-What i have to do to flash the Rom with flashtools? I found few tutorials but they are very ambiguous...
4-Is there any risk using this method?

Thanks !