Can nandroid backup be done after rooting using the revolutionary tool?


I just entered the Android world the day I purchased the HTC Sensation XE recently. :)

Straight to my query:
I recently rooted my HTC device using the revolutionary tool. So now it is "S-OFF" and has "Revolutionary" written instead of "Locked" in that screen that comes when you press down the volume key + power button. I also "flashed" the Superuser-3.0.7 file as was told in a forum ( to gain superuser access. I haven't flashed any custom ROM's as yet though.

1. Now if I wanted the ICS OTA update (stock) when it is available officially, can I update my device just like that or should I un-root it.? If so, how do I go about the un-rooting process.?

2. Also, what is this "nandroid backup" that I keep bumping into in many threads.? Is it something I should have done before rooting.?

3. How do I un-root my phone at this stage.? I read somewhere that I just need to flash the stock RUU.exe file and it'l be back to normal. But where can I find the RUU.exe file for my device. I bought my device from Kuwait, but currently using it in a different country now.

Any response to my queries would be highly appreciated. :)