N81 Software Update Questions

[risky_business]

Hi guys first time poster.

N81-1 (84.10) RM-179 0557834 (O2) software v10.0.053 [21-09-07]

I have read many posts over the last few days in respect of the process
for unbranding / software updating this phone by using Nemesis and the Nokia Software Updater.

When I enter my product (0557834) code on the Nokia Device software update site, it says

"Latest available software for Nokia N81, product code 0557834
Version: 11.0.045"

I primarily wanted to remove the O2 software branding on this phone and replace it with an
unbranded stable software version [in preference to more features].

I know that if I changed the phone's code to 0544169 with Nemesis a higher software version would be available.

"Latest available software for Nokia N81, product code 0544169
Version: 21.0.010"

A few [silly] questions if I may:

1. If I kept my N81's product code at 0557834 (ie O2 default) will the upgraded
software version [11.0.045] be unbranded. If you see what I mean.
Reason is that I was reading that v11.0.045 was broadly speaking more stable than v21.0.010.

2. On one of the Nokia Software Updater screens, it says to "ensure that a sim card is in the phone".
Is that correct? What if you receive a call or text? Does it have to be a "live" sim card ie active not expired.

3. Should the phone be reset to factory defaults prior to the software upgrade?

Any other tips to offer apart from resetting after upgrade (ie hold green / 3 / * keys until hands appear)
and should this be done with handset connected or disconnectd from pc.

Apologies for asking such stupid questions.

Many thanks for any info provided.

Cheers