Hi timethrow ,
1. In Section 4, after installing a ROM you say that we should "Wipe Cache Partition" and then "Wipe Data / Factory Reset" before and after installing the Gapps and the other files. If I did it like that, after reboot the device didn't recognize the SIM card so I had no network, I got a pop-up saying that the messaging service has crashed and if I checked the IMEI I had no number at all. I tried it once again this time without "Wipe Cache Partition" and "Wipe Data / Factory Reset". This time everything is OK. Which method is the correct one?
The first method is correct, what you did should have NO affect like that so prephaps soemthing else may be wrong. What were you upgrading from??
I had B892 Vodafone "branded" version than I upgraded via "dload" folder to B926 (Chinese), then I followed sections 0, 3 and 4 were I flashed B934 Stock repack as the official stock .zip didn't want to flash. Before reboot I did
"Wipe Cache Partition" and "Wipe Data / Factory Reset", installed all the other zips from section 4 and
"Wipe Cache Partition" and "Wipe Data / Factory Reset", once again. Reboot and than I got the error.
I did a new flash without cleaning everything and it was ok. I forgot to install the weather widget so I tried to install it after the reboot. Before rebooting, after the widget install from CWM, I cleaned everything once again. After reboot, of course that the widget was not installed, but I had the initial problem once again.
I decided to flash it once again (the stock repack B934). Before flashing, I
"Wipe Cache Partition" and "Wipe Data / Factory Reset", than I flashed the software without cleaning anything, installed all the extra .zip files that I found (I could not find go-launcher and googlenow_g300 in the ICS toolkit) without cleaning it and rebooted. Now is ok.
What did I do wrong when I got the error? Do you have any idea why I got the problem? I understand that if nobody complained about this, the procedure is correct, but were was my mistake so that I don't do it again

?
If I didn't
"Wipe Cache Partition" and "Wipe Data / Factory Reset", how it affects the device as it seems to work (no lags, restarts or crashes) ?
2. You said that is important to have all the Vodafone - Add Ons still installed as without them the OTA Upgrade WILL fail. Form where can I get all the Vodafone add-ons?
It should come bundled in with the firmware, check you have stuff like Documents to Go, Vodafone Music etc... Works on B885, B892 and B895 from a zeroed IEMI.
Are the add-ons the same for B892 from England, Italy, Romania?
3. If I want to return to the original Vodafone B892, I had on the phone, how can I unroot the device and uninstall CWM?
Zero your IEMI and then flash the B892 firmware, Update.APP file over that, CWM and Root will be removed and you will revert to stock B892.
So I zero the IMEI, the firmware is
the B892 stock .zip file which I install via CWM, right?, then
what Update.APP file I use ? After that I still have the zero IMEI. To restore the IMEI I have to root the device and restore IMEI. Then the device remains rooted. What do I do?
Sorry if the question seems dumb but this part I didn't understood it yet.
Thank you for all your help (and patience

)