None of that was an issue for me. You don’t need a Samsung account at all, you just install Firefox/Chrome/etc from the Play store and Nova allows you to customize gestures[1]. I’m not sure what you mean by “different system updates” – it just updates when an update is available.
Edit: Coincidentally, I just saw that Nova Launcher is shutting down (or has?) and folks moved to Hyperion or Octopi as their launcher of choice.
If you’re coming from Amazon’s system you’re probably learning new gestures anyway or can just set these to match the ones you know. I almost never use gestures anyway. ↩︎