Seeking clarification

Hello! I just got a new R36S and I was just curious about a few small things I am seeking claification on since I cant seem to find a proper explaination that suits my brain!

Is it absolutely needed to get a new SD card and rebuild the whole OS? Or is it just so I can add new games?

For adding new games for systems not yet listed do I add a new system folder and just copy and paste the game in it?

Is it fine for me to just leave the system alone or do I need to do all of these updates and upgrades or else it will fail?