Help To Upgrade Rom (after 7 Months) - Backup And Cookies Issues

Mar 1, 2013
Hello to you all.
I have a xiaomi mi2, and I'm currently with rom version - 4.12.5.

I didn't upgrade since miui 5 was closed (I will explain later why) and today I finally decide that it is time for me to go through that gate.

I downloaded the xiaomi.eu_multi_aries_5.7.2_v6-5.0 (this is the one I need right?),
I did a system backup using the miui backup app,
First question: Is there anything else I need to do BEFORE using the updater app to apply the upgrade?

I registered to some web service of my cellular provider about 8 months ago that let me watch some video contents. On the first visit it was required not to use WiFi - i guess for some validation - and after that I could use WiFi (or not) to get access to the videos.
I used the miui browser app when I registered and ever since I am able to watch the videos with it (I can't use other browser apps because the registration is now closed and I am getting error message that I am not a registered user).
Having saying that, this is my Sencond question: I read that it is highly recommended to wipe the user data when upgrading to miui 6, is the backup I did will be sufficient to preserve that element they are using to identify me? I believe it is a cookie but I don't know for sure. (That's why I didn't upgrade yet to MIUI 6, I was afraid to lose my registration.. stupid huh? :) )

The Third question: Where the cookies are stored on my device? I would like to try and copy them for extra safety before I apply the upgrade.

Fourth question: Regarding to the user data wipe, when do I need to do that? now, before applying the upgrade (updater app) or after the new rom is active?

Fifth question: I use the backup app pretty often (about once in a week), I have noticed that my space is running out because of that... does the backup mechanism use some sort of a diff backup and hence I must save all the backups I ever did or every backup is complete by itself and I can delete old backups?

Six (and last) question: Does the upgrade to miui 6 will erase my messages and calllogs - or anything else (so I need to use the backup to restore them) or it will be smoothly and I won't need to do anything special (just like it wast when I was updatting MIUI V5 weekly)?

Thanks a lot in advance,
I am really appreciate the great work you guys do for the world.