Updates after root


So I’m pretty sure that I won’t get OTA updates anymore after rooting my S9+ (SM-G965F/DS). So to make sure I stay current with security updates and stuff, I assume I would have to download ROM updates from sammobile.com. 2 questions:

  1. I’m in the US, bought phone on ebay. Phone originally had Singapore CSC. Should I download the Singapore ROM every time I update?

  2. Will I have to re-root after every ROM update?