[Q] things to be aware of when flashing firmwares..? topic

Hi,

I have rooted my samsung S6 set using pingpong root.
Im plagued with the battery drain issue, so i will like to revert back to stock to see if there is any OTA updates for my phone.
But to do that, i will need to unroot and then flash a stock firmware to get the ota working once again, right?

Now how do i go about choosing a firmware for my phone, seems like there are many options to be chosen from in sammy mobile webbsite.
Are there any difference between if i were to choose my country against another country version?

In what cases will i potentially brick my samsung s6?